From 5bc6e1378cd23a768d7f209f072aef5fe48bbe85 Mon Sep 17 00:00:00 2001 From: Fredric Silberberg Date: Fri, 1 Jan 2016 13:29:04 -0500 Subject: [PATCH] Readded styleguide accidentally removed in the reorg Change-Id: I240516c2c62d056e6ea4c31026918f5414c6a710 --- README.md | 2 + styleguide/cppguide.html | 2470 ++++++++++++++++++++++ styleguide/eclipse-cpp-google-style.xml | 167 ++ styleguide/eclipse-java-google-style.xml | 337 +++ styleguide/include/link.png | Bin 0 -> 189 bytes styleguide/include/styleguide.css | 261 +++ styleguide/include/styleguide.js | 289 +++ styleguide/javaguide.css | 515 +++++ styleguide/javaguide.html | 806 +++++++ styleguide/javaguidelink.png | Bin 0 -> 189 bytes styleguide/styleguide.css | 147 ++ styleguide/styleguide.xsl | 924 ++++++++ 12 files changed, 5918 insertions(+) create mode 100644 styleguide/cppguide.html create mode 100644 styleguide/eclipse-cpp-google-style.xml create mode 100644 styleguide/eclipse-java-google-style.xml create mode 100644 styleguide/include/link.png create mode 100644 styleguide/include/styleguide.css create mode 100644 styleguide/include/styleguide.js create mode 100644 styleguide/javaguide.css create mode 100644 styleguide/javaguide.html create mode 100644 styleguide/javaguidelink.png create mode 100644 styleguide/styleguide.css create mode 100644 styleguide/styleguide.xsl diff --git a/README.md b/README.md index 567b9c5675..08269834d5 100644 --- a/README.md +++ b/README.md @@ -69,3 +69,5 @@ The Simulation directory contains extra simulation tools and libraries, such as The integration test directories for C++ and Java contain test code that runs on our test-system. When you submit code for review, it is tested by those programs. If you add new functionality you should make sure to write tests for it so we don't break it in the future. The hal directory contains more C++ code meant to run on the RoboRIO. HAL is an acronym for "Hardware Abstraction Layer", and it interfaces with the NI Libraries. The NI Libraries contain the low-level code for controlling devices on your robot. The NI Libraries are found in the ni-libraries folder. + +The styleguide directory contains the styleguide for C++ and Java code. Anything submitted to the wpilib project needs to follow the code style guides outlined in there. \ No newline at end of file diff --git a/styleguide/cppguide.html b/styleguide/cppguide.html new file mode 100644 index 0000000000..f37c836c1d --- /dev/null +++ b/styleguide/cppguide.html @@ -0,0 +1,2470 @@ + + + + +WPILib C++ Style Guide + + + + +
+

WPILib C++ Style Guide (Based on the Google C++ Style Guide)

+
+ +
+ + + +

This guide is a work in progress. +We are currently working on getting this guide updated to +a point where it is useful for WPILib developers to use.

+ +

C++ is one of the two main languages (Java being the other) +used in WPILib; in order to maintain consistency and keep the +maintenance of the code manageable, we use this style guide.

+ +

There are two main overarching purposes to this guide. The first +is to act as a normal C++ style guide (both in terms fo formatting +and programming practices) for C++ developers of WPILib. +The other purpose is to help Java programmers who may +know a moderate amount of C++ but may not be fully +up to date with things like C++11 and so may not even +realize that certain C++ features exist.

+ +

This style guide is a heavily modified version of the + +Google C++ Style Guide. The Google Style Guide has +a lot of good points and is a good read, but in order +to cut the style guide down to a more readable size and to +focus mroe on WPILib-specific information, we have +altetered the original style guide in several ways.

+ +

One way in which we haven't done much to +alter the original style guide is to keep the vast +majority of the formatting/naming/etc. related +information intact. This is both so that we +do not have to write up our own standards and so +that existing tools such as clang-format and +the Google eclipse format configuration files +can work out of the box. All of these things +should be relatively non-controversial and do not +require much discussion.

+ +

Where we deviate more from the original guide is +in the style of the code itself. At the moment (ie, +when we first created this modified version), we +deleted all of the sections of the original guide +which mandate particular programming practices +such as forbidding exceptions, multiple inheritance, +etc. However, as time goes on, we gradually add in more +information along this lines, either by copying +directly from Google's Style Guide or by writing +our own decisions and best practices, some of which +may be very WPILib-specific.

+ +

As the original guide makes very clear, consistency +is extremely important to keeping the code base +manageable, and so we encourage that, wherever +reasonable, that you keep everything consistent +with whatever the standard style is.

+ +

Along with just C++ style, it is also important +to keep in mind that WPILib consists of both a C++ +and Java half. In order to keep things consistent +and easier for users, we ask that, in general, +Java and C++ be kept as consistent with one another +as reasonable. This includes everything from using +two spaces for indentation in both language to +keeping the inheritance structure essentially the +same in both. Although the two do not have to be +precisely the same, it does mean that if there is +something that you are doing which will be imposssible +to reproduce in some way in Java, then you may +want to reconsider.

+ +

One final thing to remember is that High School +students with relatively little experience programming +are the main user for this code, and throwing the full +brunt of C++ at a student just learning how to program +is likely not the best of ideas. As such, any +user-facing APIs should minimize the use of any +more complicated C++ features. As always, +use your judgement and ask others in cases where +there is something which may violate anything +in this guide.

+ +

Programming Guidelines

+

C++ is a large, complicated language, and in order +to ensure that we stay consistent and maintain certain +best practices, we have certain rules. For the most part +these are common sense rules and in some cases exist +solely to point out features of C++ that someone more +familiar with Java may not realize even exist.

+ +

Pointers

+

In general, we strongly discourage the use of +raw pointers in C++ code; instead, references or +STL pointers should be used where appropriate. +There are two exceptions to this rule:

+
    +
  • When interfacing with lower-level C code or + with any libraries which force you to use raw pointers.
    • +
  • In order to keep user interfaces consistent, + we may keep around deprecated functions which + take raw pointers. Any user-facing functions + which take raw pointers should be deprecated + using the + [[deprecated]] + attribute and replaced with either references + or STL pointers.
    • +
+

As of C++11, the following are options in the +place of raw pointers:

+
    +
  • std::unique_ptr Should be used + when you still need to use a pointer, but you + only need one entity to own the pointer. The + std::unique_ptr will automatically + be deleted when there are no more references to + it.
    • +
  • std::shared_ptr Should be used + when you still need to use a pointer and you + need many references to the object. When + there are zero remaining references to the + object, it will be deleted. Use std::weak_ptr + where necessary to avoid circular dependencies + or other potential issues.
    • +
  • L-value references (the traditional sort + of reference that has been around since before C++11) + should be used when you want to pass around a + reference to an object and want to guarantee + that it won't be null. Use const references + if you want to avoid copying a large object + but don't want to modify it.
    • +
  • R-value references were introduced in C++11 + and allow for the use of std::move. + R-value references should be used where it makes + sense that a parameter to a function is having + its ownership passed from one place to another. + In general, R-value references are not inherently + bad, but they do introduce additional complexity + that may confuse people who are not familiar + with them.
    • +
+ +

Deprecation

+

When updating APIs, make liberal use of the +[[deprecated]] attribute (although if +it is reasonable to simply remove any old interfaces +then do so) to indicate that users should no longer +use the function. Currently, this will cause warnings +in user code and errors in the WPILib build.

+ +
+[[deprecated("This is a deprecated function; this text will be displayed when"
+             " the compiler throws a warning.")]]
+void foo() {}
+class [[deprecated("This is a deprecated class.")]] Foo {};
+int bar [[deprecated("This is a deprecated variable.")]];
+
+ +

See +here for more information on deprecation.

+ +

Header Files

+ +

In general, every .cc file should have an +associated .h file. There are some common +exceptions, such as unittests and +small .cpp files containing just a +main() function.

+ +

Correct use of header files can make a huge difference to +the readability, size and performance of your code.

+ +

The following rules will guide you through the various +pitfalls of using header files.

+ + +

Self-contained Headers

+ +
+

Header files should be self-contained and end in .h. Files that +are meant for textual inclusion, but are not headers, should end in +.inc. Separate -inl.h headers are disallowed.

+
+ +
+

All header files should be self-contained. In other +words, users and refactoring tools should not have to adhere to special +conditions in order to include the header. Specifically, a +header should have header guards, +should include all other headers it needs, and should not require any +particular symbols to be defined.

+ +

There are rare cases where a file is not meant to be self-contained, but +instead is meant to be textually included at a specific point in the code. +Examples are files that need to be included multiple times or +platform-specific extensions that essentially are part of other headers. Such +files should use the file extension .inc.

+ +

If a template or inline function is declared in a .h file, +define it in that same file. The definitions of these constructs must +be included into every .cc file that uses them, or the +program may fail to link in some build configurations. Do not move these +definitions to separate -inl.h files.

+ +

As an exception, a function template that is explicitly +instantiated for all relevant sets of template arguments, or +that is a private member of a class, may +be defined in the only .cc file that +instantiates the template.

+ +
+ +

The #define Guard

+ +
+

All header files should have #define guards to +prevent multiple inclusion. The format of the symbol name +should be +<PROJECT>_<PATH>_<FILE>_H_.

+
+ +
+ + + +

To guarantee uniqueness, they should +be based on the full path in a project's source tree. For +example, the file foo/src/bar/baz.h in +project foo should have the following +guard:

+ +
#ifndef FOO_BAR_BAZ_H_
+#define FOO_BAR_BAZ_H_
+
+...
+
+#endif  // FOO_BAR_BAZ_H_
+
+ + + + +
+ +

Forward Declarations

+ +
+

You may forward declare ordinary classes in order to avoid +unnecessary #includes.

+
+ +
+ +
+

A "forward declaration" is a declaration of a class, +function, or template without an associated definition. +#include lines can often be replaced with +forward declarations of whatever symbols are actually +used by the client code.

+
+ +
+
    +
  • Unnecessary #includes force the + compiler to open more files and process more + input.
    • + +
  • They can also force your code to be recompiled more + often, due to changes in the header.
    • +
+
+ +
+
    +
  • It can be difficult to determine the correct form + of a forward declaration in the presence of features + like templates, typedefs, default parameters, and using + declarations.
    • + +
  • It can be difficult to determine whether a forward + declaration or a full #include is needed + for a given piece of code, particularly when implicit + conversion operations are involved. In extreme cases, + replacing an #include with a forward + declaration can silently change the meaning of + code.
    • + +
  • Forward declaring multiple symbols from a header + can be more verbose than simply + #includeing the header.
    • + +
  • Forward declarations of functions and templates can + prevent the header owners from making + otherwise-compatible changes to their APIs; for + example, widening a parameter type, or adding a + template parameter with a default value.
    • +
  • Forward declaring symbols from namespace + std:: usually yields undefined + behavior.
    • + +
  • Structuring code to enable forward declarations + (e.g. using pointer members instead of object members) + can make the code slower and more complex.
    • + +
  • The practical efficiency benefits of forward + declarations are unproven.
    • +
+
+ +
+
    +
  • When using a function declared in a header file, + always #include that header.
    • + +
  • When using a class template, prefer to + #include its header file.
    • + +
  • When using an ordinary class, relying on a forward + declaration is OK, but be wary of situations where a + forward declaration may be insufficient or incorrect; + when in doubt, just #include the + appropriate header.
    • + +
  • Do not replace data members with pointers just to + avoid an #include.
    • +
+ +

Please see Names and Order +of Includes for rules about when to #include a header.

+
+ +
+ +

Inline Functions

+ +
+

Define functions inline only when they are small, say, 10 +lines or less.

+
+ +
+ +
+

You can declare functions in a way that allows the compiler to expand +them inline rather than calling them through the usual +function call mechanism.

+
+ +
+

Inlining a function can generate more efficient object +code, as long as the inlined function is small. Feel free +to inline accessors and mutators, and other short, +performance-critical functions.

+
+ +
+

Overuse of inlining can actually make programs slower. +Depending on a function's size, inlining it can cause the +code size to increase or decrease. Inlining a very small +accessor function will usually decrease code size while +inlining a very large function can dramatically increase +code size. On modern processors smaller code usually runs +faster due to better use of the instruction cache.

+
+ +
+

A decent rule of thumb is to not inline a function if +it is more than 10 lines long. Beware of destructors, +which are often longer than they appear because of +implicit member- and base-destructor calls!

+ +

Another useful rule of thumb: it's typically not cost +effective to inline functions with loops or switch +statements (unless, in the common case, the loop or +switch statement is never executed).

+ +

It is important to know that functions are not always +inlined even if they are declared as such; for example, +virtual and recursive functions are not normally inlined. +Usually recursive functions should not be inline. The +main reason for making a virtual function inline is to +place its definition in the class, either for convenience +or to document its behavior, e.g., for accessors and +mutators.

+
+ +
+ +

Function Parameter Ordering

+ +
+

When defining a function, parameter order is: inputs, then +outputs.

+
+ +
+

Parameters to C/C++ functions are either input to the +function, output from the function, or both. Input +parameters are usually values or const +references, while output and input/output parameters will +be non-const pointers. When ordering +function parameters, put all input-only parameters before +any output parameters. In particular, do not add new +parameters to the end of the function just because they +are new; place new input-only parameters before the +output parameters.

+ +

This is not a hard-and-fast rule. Parameters that are +both input and output (often classes/structs) muddy the +waters, and, as always, consistency with related +functions may require you to bend the rule.

+ +
+ +

Names and Order of Includes

+ +
+

Use standard order for readability and to avoid hidden +dependencies: Related header, C library, C++ library, other libraries' +.h, your project's .h.

+
+ +
+

+All of a project's header files should be +listed as descendants of the project's source +directory without use of UNIX directory shortcuts +. (the current directory) or .. +(the parent directory). For example, + +google-awesome-project/src/base/logging.h +should be included as:

+ +
#include "base/logging.h"
+
+ +

In dir/foo.cc or +dir/foo_test.cc, whose main +purpose is to implement or test the stuff in +dir2/foo2.h, order your includes +as follows:

+ +
    +
  1. dir2/foo2.h.
    2. + +
  2. C system files.
    3. + +
  3. C++ system files.
    4. + +
  4. Other libraries' .h + files.
    5. + +
  5. + Your project's .h + files.
    6. +
+ +

With the preferred ordering, if +dir2/foo2.h omits any necessary +includes, the build of dir/foo.cc +or dir/foo_test.cc will break. +Thus, this rule ensures that build breaks show up first +for the people working on these files, not for innocent +people in other packages.

+ +

dir/foo.cc and +dir2/foo2.h are usually in the same +directory (e.g. base/basictypes_test.cc and +base/basictypes.h), but may sometimes be in different +directories too.

+ + + +

Within each section the includes should be ordered +alphabetically. Note that older code might not conform to +this rule and should be fixed when convenient.

+ +

You should include all the headers that define the symbols you rely +upon (except in cases of forward +declaration). If you rely on symbols from bar.h, +don't count on the fact that you included foo.h which +(currently) includes bar.h: include bar.h +yourself, unless foo.h explicitly demonstrates its intent +to provide you the symbols of bar.h. However, any +includes present in the related header do not need to be included +again in the related cc (i.e., foo.cc can +rely on foo.h's includes).

+ +

For example, the includes in + +google-awesome-project/src/foo/internal/fooserver.cc +might look like this:

+ + +
#include "foo/server/fooserver.h"
+
+#include <sys/types.h>
+#include <unistd.h>
+#include <hash_map>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/commandlineflags.h"
+#include "foo/server/bar.h"
+
+ +

Sometimes, system-specific code needs +conditional includes. Such code can put conditional +includes after other includes. Of course, keep your +system-specific code small and localized. Example:

+ +
#include "foo/public/fooserver.h"
+
+#include "base/port.h"  // For LANG_CXX11.
+
+#ifdef LANG_CXX11
+#include <initializer_list>
+#endif  // LANG_CXX11
+
+ +
+ +

Naming

+ +

The most important consistency rules are those that govern +naming. The style of a name immediately informs us what sort of +thing the named entity is: a type, a variable, a function, a +constant, a macro, etc., without requiring us to search for the +declaration of that entity. The pattern-matching engine in our +brains relies a great deal on these naming rules. +

+ +

Naming rules are pretty arbitrary, but + we feel that +consistency is more important than individual preferences in this +area, so regardless of whether you find them sensible or not, +the rules are the rules.

+ +

General Naming Rules

+ +
+

Function names, variable names, and filenames should be +descriptive; eschew abbreviation.

+
+ +
+

Give as descriptive a name as possible, within reason. +Do not worry about saving horizontal space as it is far +more important to make your code immediately +understandable by a new reader. Do not use abbreviations +that are ambiguous or unfamiliar to readers outside your +project, and do not abbreviate by deleting letters within +a word.

+ +
int price_count_reader;    // No abbreviation.
+int num_errors;            // "num" is a widespread convention.
+int num_dns_connections;   // Most people know what "DNS" stands for.
+
+ +
int n;                     // Meaningless.
+int nerr;                  // Ambiguous abbreviation.
+int n_comp_conns;          // Ambiguous abbreviation.
+int wgc_connections;       // Only your group knows what this stands for.
+int pc_reader;             // Lots of things can be abbreviated "pc".
+int cstmr_id;              // Deletes internal letters.
+
+ +
+ +

File Names

+ +
+

Filenames should be all lowercase and can include +underscores (_) or dashes (-). +Follow the convention that your + +project uses. If there is no consistent +local pattern to follow, prefer "_".

+
+ +
+ +

Examples of acceptable file names:

+ +
    +
  • my_useful_class.cc
    • +
  • my-useful-class.cc
    • +
  • myusefulclass.cc
    • +
  • myusefulclass_test.cc // _unittest and _regtest are deprecated.
    • +
+ +

C++ files should end in .cc and header files should end in +.h. Files that rely on being textually included at specific points +should end in .inc (see also the section on +self-contained headers).

+ +

Do not use filenames that already exist in +/usr/include, such as db.h.

+ +

In general, make your filenames very specific. For +example, use http_server_logs.h rather than +logs.h. A very common case is to have a pair +of files called, e.g., foo_bar.h and +foo_bar.cc, defining a class called +FooBar.

+ +

Inline functions must be in a .h file. If +your inline functions are very short, they should go +directly into your .h file.

+ +
+ +

Type Names

+ +
+

Type names start with a capital letter and have a capital +letter for each new word, with no underscores: +MyExcitingClass, MyExcitingEnum.

+
+ +
+ +

The names of all types — classes, structs, typedefs, +and enums — have the same naming convention. Type names +should start with a capital letter and have a capital letter +for each new word. No underscores. For example:

+ +
// classes and structs
+class UrlTable { ...
+class UrlTableTester { ...
+struct UrlTableProperties { ...
+
+// typedefs
+typedef hash_map<UrlTableProperties *, string> PropertiesMap;
+
+// enums
+enum UrlTableErrors { ...
+
+ +
+ +

Variable Names

+ +
+

The names of variables and data members are all lowercase, with +underscores between words. Data members of classes (but not structs) +additionally are prefixed with "m_". For instance: +a_local_variable, a_struct_data_member, +m_a_class_data_member.

+
+ +
+ +

Common Variable names

+ +

For example:

+ +
string table_name;  // OK - uses underscore.
+string tablename;   // OK - all lowercase.
+
+ +
string tableName;   // Bad - mixed case.
+
+ +

Class Data Members

+ +

Data members of classes, both static and non-static, are +named like ordinary nonmember variables, but prefixed with a +"m_".

+ +
class TableInfo {
+  ...
+ private:
+  string m_table_name;  // OK - m_ at beginning.
+  string m_tablename;   // OK.
+  static Pool<TableInfo>* m_pool;  // OK.
+};
+
+ +

Struct Data Members

+ +

Data members of structs, both static and non-static, +are named like ordinary nonmember variables. They do not have +the preceding "m_" that data members in classes have.

+ +
struct UrlTableProperties {
+  string name;
+  int num_entries;
+  static Pool<UrlTableProperties>* pool;
+};
+
+ + +

See Structs vs. +Classes for a discussion of when to use a struct +versus a class.

+ +

Global Variables

+ +

There are no special requirements for global +variables, which should be rare in any case, but if you +use one, consider prefixing it with g_ or +some other marker to easily distinguish it from local +variables.

+ +
+ +

Constant Names

+ +
+

Use a k followed by mixed case, e.g., +kDaysInAWeek, for constants defined globally or within a class.

+
+ +
+ +

As a convenience to the reader, compile-time constants of global or class scope +follow a different naming convention from other variables. +Use a k followed by words with uppercase first letters:

+ +
const int kDaysInAWeek = 7;
+
+ +

This convention may optionally be used for compile-time constants of local scope; +otherwise the usual variable naming rules apply. + +

+ +

Function Names

+ +
+

Regular functions have mixed case; accessors and mutators +match the name of the variable: +MyExcitingFunction(), +MyExcitingMethod(), +my_exciting_member_variable(), +set_my_exciting_member_variable().

+
+ +
+ +

Regular Functions

+ +

Functions should start with a capital letter and have +a capital letter for each new word. No underscores.

+ +

If your function crashes upon an error, you should +append OrDie to the function name. This only applies to +functions which could be used by production code and to +errors that are reasonably likely to occur during normal +operation.

+ + 
AddTableEntry()
+DeleteUrl()
+OpenFileOrDie()
+
+ +

Accessors and Mutators

+ +

Accessors and mutators (get and set functions) should +match the name of the variable they are getting and +setting. This shows an excerpt of a class whose instance +variable is num_entries_.

+ +
class MyClass {
+ public:
+  ...
+  int num_entries() const { return num_entries_; }
+  void set_num_entries(int num_entries) { num_entries_ = num_entries; }
+
+ private:
+  int num_entries_;
+};
+
+ +

You may also use lowercase letters for other very +short inlined functions. For example if a function were +so cheap you would not cache the value if you were +calling it in a loop, then lowercase naming would be +acceptable.

+ +
+ +

Namespace Names

+ +
+ + +

Namespace names are all lower-case, +and based on project names and possibly their directory +structure: google_awesome_project.

+
+ +
+ +

See Namespaces for a +discussion of namespaces and how to name them.

+ +
+ +

Enumerator Names

+ +
+

Enumerators should be named either like +constants or like +macros: either kEnumName or +ENUM_NAME.

+
+ +
+ +

Preferably, the individual enumerators should be named +like constants. However, it +is also acceptable to name them like +macros. The enumeration name, +UrlTableErrors (and +AlternateUrlTableErrors), is a type, and +therefore mixed case.

+ +
enum UrlTableErrors {
+  kOK = 0,
+  kErrorOutOfMemory,
+  kErrorMalformedInput,
+};
+enum AlternateUrlTableErrors {
+  OK = 0,
+  OUT_OF_MEMORY = 1,
+  MALFORMED_INPUT = 2,
+};
+
+ +

Until January 2009, the style was to name enum values +like macros. This caused +problems with name collisions between enum values and +macros. Hence, the change to prefer constant-style naming +was put in place. New code should prefer constant-style +naming if possible. However, there is no reason to change +old code to use constant-style names, unless the old +names are actually causing a compile-time problem.

+ + + +
+ +

Macro Names

+ +
+

You're not really going to +define a macro, are you? If you do, they're like this: +MY_MACRO_THAT_SCARES_SMALL_CHILDREN.

+
+ +
+ +

Please see the description +of macros; in general macros should not be used. +However, if they are absolutely needed, then they should be +named with all capitals and underscores.

+ +
#define ROUND(x) ...
+#define PI_ROUNDED 3.0
+
+ +
+ +

Exceptions to Naming Rules

+ +
+

If you are naming something that is analogous to an +existing C or C++ entity then you can follow the existing +naming convention scheme.

+
+ +
+ +
+
bigopen()
+
function name, follows form of open()
+ +
uint
+
typedef
+ +
bigpos
+
struct or class, follows + form of pos
+ +
sparse_hash_map
+
STL-like entity; follows STL naming conventions
+ +
LONGLONG_MAX
+
a constant, as in INT_MAX
+
+ +
+ +

Comments

+ +

Though a pain to write, comments are absolutely vital to +keeping our code readable. The following rules describe what +you should comment and where. But remember: while comments are +very important, the best code is self-documenting. Giving +sensible names to types and variables is much better than using +obscure names that you must then explain through comments.

+ +

When writing your comments, write for your audience: the +next +contributor who will need to +understand your code. Be generous — the next +one may be you!

+ +

Comment Style

+ +
+

Use either the // or /* */ +syntax, as long as you are consistent.

+
+ +
+ +

You can use either the // or the /* +*/ syntax; however, // is +much more common. Be consistent with how you +comment and what style you use where.

+ +
+ +

File Comments

+ +
+

Start each file with license +boilerplate, followed by a description of its +contents.

+
+ +
+ +

Legal Notice and Author +Line

+ + + +

Every file should contain license +boilerplate. Choose the appropriate boilerplate for the +license used by the project (for example, Apache 2.0, +BSD, LGPL, GPL).

+ +

If you make significant changes to a file with an +author line, consider deleting the author line.

+ +

File Contents

+ +

Every file should have a comment at the top describing +its contents.

+ +

Generally a .h file will describe the +classes that are declared in the file with an overview of +what they are for and how they are used. A +.cc file should contain more information +about implementation details or discussions of tricky +algorithms. If you feel the implementation details or a +discussion of the algorithms would be useful for someone +reading the .h, feel free to put it there +instead, but mention in the .cc that the +documentation is in the .h file.

+ +

Do not duplicate comments in both the .h +and the .cc. Duplicated comments +diverge.

+ +
+ +

Class Comments

+ +
+

Every class definition should have an accompanying comment +that describes what it is for and how it should be used.

+
+ +
+ +
// Iterates over the contents of a GargantuanTable.  Sample usage:
+//    GargantuanTableIterator* iter = table->NewIterator();
+//    for (iter->Seek("foo"); !iter->done(); iter->Next()) {
+//      process(iter->key(), iter->value());
+//    }
+//    delete iter;
+class GargantuanTableIterator {
+  ...
+};
+
+ +

If you have already described a class in detail in the +comments at the top of your file feel free to simply +state "See comment at top of file for a complete +description", but be sure to have some sort of +comment.

+ +

Document the synchronization assumptions the class +makes, if any. If an instance of the class can be +accessed by multiple threads, take extra care to document +the rules and invariants surrounding multithreaded +use.

+ +
+ +

Function Comments

+ +
+

Declaration comments describe use of the function; comments +at the definition of a function describe operation.

+
+ +
+ +

Function Declarations

+ +

Every function declaration should have comments +immediately preceding it that describe what the function +does and how to use it. These comments should be +descriptive ("Opens the file") rather than imperative +("Open the file"); the comment describes the function, it +does not tell the function what to do. In general, these +comments do not describe how the function performs its +task. Instead, that should be left to comments in the +function definition.

+ +

Types of things to mention in comments at the function +declaration:

+ +
    +
  • What the inputs and outputs are.
    • + +
  • For class member functions: whether the object + remembers reference arguments beyond the duration of + the method call, and whether it will free them or + not.
    • + +
  • If the function allocates memory that the caller + must free.
    • + +
  • Whether any of the arguments can be a null + pointer.
    • + +
  • If there are any performance implications of how a + function is used.
    • + +
  • If the function is re-entrant. What are its + synchronization assumptions?
    • +
+ +

Here is an example:

+ +
// Returns an iterator for this table.  It is the client's
+// responsibility to delete the iterator when it is done with it,
+// and it must not use the iterator once the GargantuanTable object
+// on which the iterator was created has been deleted.
+//
+// The iterator is initially positioned at the beginning of the table.
+//
+// This method is equivalent to:
+//    Iterator* iter = table->NewIterator();
+//    iter->Seek("");
+//    return iter;
+// If you are going to immediately seek to another place in the
+// returned iterator, it will be faster to use NewIterator()
+// and avoid the extra seek.
+Iterator* GetIterator() const;
+
+ +

However, do not be unnecessarily verbose or state the +completely obvious. Notice below that it is not necessary + to say "returns false otherwise" because this is +implied.

+ +
// Returns true if the table cannot hold any more entries.
+bool IsTableFull();
+
+ +

When commenting constructors and destructors, remember +that the person reading your code knows what constructors +and destructors are for, so comments that just say +something like "destroys this object" are not useful. +Document what constructors do with their arguments (for +example, if they take ownership of pointers), and what +cleanup the destructor does. If this is trivial, just +skip the comment. It is quite common for destructors not +to have a header comment.

+ +

Function Definitions

+ +

If there is anything tricky about how a function does +its job, the function definition should have an +explanatory comment. For example, in the definition +comment you might describe any coding tricks you use, +give an overview of the steps you go through, or explain +why you chose to implement the function in the way you +did rather than using a viable alternative. For instance, +you might mention why it must acquire a lock for the +first half of the function but why it is not needed for +the second half.

+ +

Note you should not just repeat the comments +given with the function declaration, in the +.h file or wherever. It's okay to +recapitulate briefly what the function does, but the +focus of the comments should be on how it does it.

+ +
+ +

Variable Comments

+ +
+

In general the actual name of the variable should be +descriptive enough to give a good idea of what the variable +is used for. In certain cases, more comments are required.

+
+ +
+ +

Class Data Members

+ +

Each class data member (also called an instance +variable or member variable) should have a comment +describing what it is used for. If the variable can take +sentinel values with special meanings, such as a null +pointer or -1, document this. For example:

+ + +
private:
+ // Keeps track of the total number of entries in the table.
+ // Used to ensure we do not go over the limit. -1 means
+ // that we don't yet know how many entries the table has.
+ int num_total_entries_;
+
+ +

Global Variables

+ +

As with data members, all global variables should have +a comment describing what they are and what they are used +for. For example:

+ +
// The total number of tests cases that we run through in this regression test.
+const int kNumTestCases = 6;
+
+ +
+ +

Implementation Comments

+ +
+

In your implementation you should have comments in tricky, +non-obvious, interesting, or important parts of your code.

+
+ +
+ +

Explanatory Comments

+ +

Tricky or complicated code blocks should have comments +before them. Example:

+ +
// Divide result by two, taking into account that x
+// contains the carry from the add.
+for (int i = 0; i < result->size(); i++) {
+  x = (x << 8) + (*result)[i];
+  (*result)[i] = x >> 1;
+  x &= 1;
+}
+
+ +

Line Comments

+ +

Also, lines that are non-obvious should get a comment +at the end of the line. These end-of-line comments should +be separated from the code by 2 spaces. Example:

+ +
// If we have enough memory, mmap the data portion too.
+mmap_budget = max<int64>(0, mmap_budget - index_->length());
+if (mmap_budget >= data_size_ && !MmapData(mmap_chunk_bytes, mlock))
+  return;  // Error already logged.
+
+ +

Note that there are both comments that describe what +the code is doing, and comments that mention that an +error has already been logged when the function +returns.

+ +

If you have several comments on subsequent lines, it +can often be more readable to line them up:

+ +
DoSomething();                  // Comment here so the comments line up.
+DoSomethingElseThatIsLonger();  // Two spaces between the code and the comment.
+{ // One space before comment when opening a new scope is allowed,
+  // thus the comment lines up with the following comments and code.
+  DoSomethingElse();  // Two spaces before line comments normally.
+}
+vector<string> list{// Comments in braced lists describe the next element ..
+                    "First item",
+                    // .. and should be aligned appropriately.
+                    "Second item"};
+DoSomething(); /* For trailing block comments, one space is fine. */
+
+ +

nullptr/NULL, true/false, 1, 2, 3...

+ +

When you pass in a null pointer, boolean, or literal +integer values to functions, you should consider adding a +comment about what they are, or make your code +self-documenting by using constants. For example, +compare:

+ +
bool success = CalculateSomething(interesting_value,
+                                  10,
+                                  false,
+                                  NULL);  // What are these arguments??
+
+ +

versus:

+ +
bool success = CalculateSomething(interesting_value,
+                                  10,     // Default base value.
+                                  false,  // Not the first time we're calling this.
+                                  NULL);  // No callback.
+
+ +

Or alternatively, constants or self-describing variables:

+ +
const int kDefaultBaseValue = 10;
+const bool kFirstTimeCalling = false;
+Callback *null_callback = NULL;
+bool success = CalculateSomething(interesting_value,
+                                  kDefaultBaseValue,
+                                  kFirstTimeCalling,
+                                  null_callback);
+
+ +

Don'ts

+ +

Note that you should never describe the code +itself. Assume that the person reading the code knows C++ +better than you do, even though he or she does not know +what you are trying to do:

+ +
// Now go through the b array and make sure that if i occurs,
+// the next element is i+1.
+...        // Geez.  What a useless comment.
+
+ +
+ +

Punctuation, Spelling and Grammar

+ +
+

Pay attention to punctuation, spelling, and grammar; it is +easier to read well-written comments than badly written +ones.

+
+ +
+ +

Comments should be as readable as narrative text, with +proper capitalization and punctuation. In many cases, +complete sentences are more readable than sentence +fragments. Shorter comments, such as comments at the end +of a line of code, can sometimes be less formal, but you +should be consistent with your style.

+ +

Although it can be frustrating to have a code reviewer +point out that you are using a comma when you should be +using a semicolon, it is very important that source code +maintain a high level of clarity and readability. Proper +punctuation, spelling, and grammar help with that +goal.

+ +
+ +

TODO Comments

+ +
+

Use TODO comments for code that is temporary, +a short-term solution, or good-enough but not perfect.

+
+ +
+ +

TODOs should include the string +TODO in all caps, followed by the + +name, e-mail address, or other +identifier of the person + with the best context +about the problem referenced by the TODO. The +main purpose is to have a consistent TODO that +can be searched to find out how to get more details upon +request. A TODO is not a commitment that the +person referenced will fix the problem. Thus when you create +a TODO, it is almost always your + +name +that is given.

+ + + +
+
// TODO(kl@gmail.com): Use a "*" here for concatenation operator.
+// TODO(Zeke) change this to use relations.
+
+
+ +

If your TODO is of the form "At a future +date do something" make sure that you either include a +very specific date ("Fix by November 2005") or a very +specific event ("Remove this code when all clients can +handle XML responses.").

+ +
+ +

Deprecation Comments

+ +
+

Mark deprecated interface points with DEPRECATED +comments.

+
+ +
+ +

You can mark an interface as deprecated by writing a +comment containing the word DEPRECATED in +all caps. The comment goes either before the declaration +of the interface or on the same line as the +declaration.

+ + + +

After the word +DEPRECATED, write your name, e-mail address, +or other identifier in parentheses.

+ +

A deprecation comment must include simple, clear +directions for people to fix their callsites. In C++, you +can implement a deprecated function as an inline function +that calls the new interface point.

+ +

Marking an interface point DEPRECATED +will not magically cause any callsites to change. If you +want people to actually stop using the deprecated +facility, you will have to fix the callsites yourself or +recruit a crew to help you.

+ +

New code should not contain calls to deprecated +interface points. Use the new interface point instead. If +you cannot understand the directions, find the person who +created the deprecation and ask them for help using the +new interface point.

+ + + +
+ +

Formatting

+ +

Coding style and formatting are pretty arbitrary, but a + +project is much easier to follow +if everyone uses the same style. Individuals may not agree with every +aspect of the formatting rules, and some of the rules may take +some getting used to, but it is important that all + +project contributors follow the +style rules so that +they can all read and understand +everyone's code easily.

+ + + +

To help you format code correctly, we've +created a + +settings file for emacs.

+ +

Line Length

+ +
+

Each line of text in your code should be at most 80 +characters long.

+
+ +
+ + + +

We recognize that this rule is +controversial, but so much existing code already adheres +to it, and we feel that consistency is important.

+ +
+

Those who favor this rule +argue that it is rude to force them to resize +their windows and there is no need for anything longer. +Some folks are used to having several code windows +side-by-side, and thus don't have room to widen their +windows in any case. People set up their work environment +assuming a particular maximum window width, and 80 +columns has been the traditional standard. Why change +it?

+
+ +
+

Proponents of change argue that a wider line can make +code more readable. The 80-column limit is an hidebound +throwback to 1960s mainframes; modern equipment has wide screens that +can easily show longer lines.

+
+ +
+

80 characters is the maximum.

+ +

If a comment line contains an example +command or a literal URL longer than 80 characters, that +line may be longer than 80 characters for ease of cut and +paste.

+ +

A raw-string literal may have content +that exceeds 80 characters. Except for test code, such literals +should appear near top of a file.

+ +

An #include statement with a +long path may exceed 80 columns.

+ +

You needn't be concerned about +header guards that exceed +the maximum length.

+
+ +
+ +

Non-ASCII Characters

+ +
+

Non-ASCII characters should be rare, and must use UTF-8 +formatting.

+
+ +
+ +

You shouldn't hard-code user-facing text in source, +even English, so use of non-ASCII characters should be +rare. However, in certain cases it is appropriate to +include such words in your code. For example, if your +code parses data files from foreign sources, it may be +appropriate to hard-code the non-ASCII string(s) used in +those data files as delimiters. More commonly, unittest +code (which does not need to be localized) might +contain non-ASCII strings. In such cases, you should use +UTF-8, since that is an encoding +understood by most tools able to handle more than just +ASCII.

+ +

Hex encoding is also OK, and encouraged where it +enhances readability — for example, +"\xEF\xBB\xBF", or, even more simply, +u8"\uFEFF", is the Unicode zero-width +no-break space character, which would be invisible if +included in the source as straight UTF-8.

+ +

Use the u8 prefix +to guarantee that a string literal containing +\uXXXX escape sequences is encoded as UTF-8. +Do not use it for strings containing non-ASCII characters +encoded as UTF-8, because that will produce incorrect +output if the compiler does not interpret the source file +as UTF-8.

+ +

You shouldn't use the C++11 char16_t and +char32_t character types, since they're for +non-UTF-8 text. For similar reasons you also shouldn't +use wchar_t (unless you're writing code that +interacts with the Windows API, which uses +wchar_t extensively).

+ +
+ +

Spaces vs. Tabs

+ +
+

Use only spaces, and indent 2 spaces at a time.

+
+ +
+ +

We use spaces for indentation. Do not use tabs in your +code. You should set your editor to emit spaces when you +hit the tab key.

+ +
+ +

Function Declarations and Definitions

+ +
+

Return type on the same line as function name, parameters +on the same line if they fit. Wrap parameter lists which do +not fit on a single line as you would wrap arguments in a +function call.

+
+ +
+ +

Functions look like this:

+ + +
ReturnType ClassName::FunctionName(Type par_name1, Type par_name2) {
+  DoSomething();
+  ...
+}
+
+ +

If you have too much text to fit on one line:

+ +
ReturnType ClassName::ReallyLongFunctionName(Type par_name1, Type par_name2,
+                                             Type par_name3) {
+  DoSomething();
+  ...
+}
+
+ +

or if you cannot fit even the first parameter:

+ +
ReturnType LongClassName::ReallyReallyReallyLongFunctionName(
+    Type par_name1,  // 4 space indent
+    Type par_name2,
+    Type par_name3) {
+  DoSomething();  // 2 space indent
+  ...
+}
+
+ +

Some points to note:

+ +
    +
  • If you cannot fit the return type and the function + name on a single line, break between them.
    • + +
  • If you break after the return type of a function + declaration or definition, do not indent.
    • + +
  • The open parenthesis is always on the same line as + the function name.
    • + +
  • There is never a space between the function name + and the open parenthesis.
    • + +
  • There is never a space between the parentheses and + the parameters.
    • + +
  • The open curly brace is always at the end of the + same line as the last parameter.
    • + +
  • The close curly brace is either on the last line by + itself or (if other style rules permit) on the same + line as the open curly brace.
    • + +
  • There should be a space between the close + parenthesis and the open curly brace.
    • + +
  • All parameters should be named, with identical + names in the declaration and implementation.
    • + +
  • All parameters should be aligned if possible.
    • + +
  • Default indentation is 2 spaces.
    • + +
  • Wrapped parameters have a 4 space indent.
    • +
+ +

If some parameters are unused, comment out the +variable name in the function definition:

+ +
// Always have named parameters in interfaces.
+class Shape {
+ public:
+  virtual void Rotate(double radians) = 0;
+};
+
+// Always have named parameters in the declaration.
+class Circle : public Shape {
+ public:
+  virtual void Rotate(double radians);
+};
+
+// Comment out unused named parameters in definitions.
+void Circle::Rotate(double /*radians*/) {}
+
+ +
// Bad - if someone wants to implement later, it's not clear what the
+// variable means.
+void Circle::Rotate(double) {}
+
+ +
+ +

Lambda Expressions

+ +
+

Format parameters and bodies as for any other function, and capture +lists like other comma-separated lists.

+
+ +
+

For by-reference captures, do not leave a space between the +ampersand (&) and the variable name.

+
int x = 0;
+auto add_to_x = [&x](int n) { x += n; };
+
+

Short lambdas may be written inline as function arguments.

+
std::set<int> blacklist = {7, 8, 9};
+std::vector<int> digits = {3, 9, 1, 8, 4, 7, 1};
+digits.erase(std::remove_if(digits.begin(), digits.end(), [&blacklist](int i) {
+               return blacklist.find(i) != blacklist.end();
+             }),
+             digits.end());
+
+ +
+ +

Function Calls

+ +
+

Either write the call all on a single line, wrap the +arguments at the parenthesis, or start the arguments on a new +line indented by four spaces and continue at that 4 space +indent. In the absence of other considerations, use the +minimum number of lines, including placing multiple arguments +on each line where appropriate.

+
+ +
+ +

Function calls have the following format:

+
bool retval = DoSomething(argument1, argument2, argument3);
+
+ +

If the arguments do not all fit on one line, they +should be broken up onto multiple lines, with each +subsequent line aligned with the first argument. Do not +add spaces after the open paren or before the close +paren:

+
bool retval = DoSomething(averyveryveryverylongargument1,
+                          argument2, argument3);
+
+ +

Arguments may optionally all be placed on subsequent +lines with a four space indent:

+
if (...) {
+  ...
+  ...
+  if (...) {
+    DoSomething(
+        argument1, argument2,  // 4 space indent
+        argument3, argument4);
+  }
+
+ +

Put multiple arguments on a single line to reduce the +number of lines necessary for calling a function unless +there is a specific readability problem. Some find that +formatting with strictly one argument on each line is +more readable and simplifies editing of the arguments. +However, we prioritize for the reader over the ease of +editing arguments, and most readability problems are +better addressed with the following techniques.

+ +

If having multiple arguments in a single line decreases +readability due to the complexity or confusing nature of the +expressions that make up some arguments, try creating +variables that capture those arguments in a descriptive name:

+
int my_heuristic = scores[x] * y + bases[x];
+bool retval = DoSomething(my_heuristic, x, y, z);
+
+ +

Or put the confusing argument on its own line with +an explanatory comment:

+
bool retval = DoSomething(scores[x] * y + bases[x],  // Score heuristic.
+                          x, y, z);
+
+ +

If there is still a case where one argument is +significantly more readable on its own line, then put it on +its own line. The decision should be specific to the argument +which is made more readable rather than a general policy.

+ +

Sometimes arguments form a structure that is important +for readability. In those cases, feel free to format the +arguments according to that structure:

+
// Transform the widget by a 3x3 matrix.
+my_widget.Transform(x1, x2, x3,
+                    y1, y2, y3,
+                    z1, z2, z3);
+
+ +
+ +

Braced Initializer List Format

+ +
+

Format a braced initializer list +exactly like you would format a function call in its place.

+
+ +
+ +

If the braced list follows a name (e.g. a type or +variable name), format as if the {} were the +parentheses of a function call with that name. If there +is no name, assume a zero-length name.

+ +
// Examples of braced init list on a single line.
+return {foo, bar};
+functioncall({foo, bar});
+pair<int, int> p{foo, bar};
+
+// When you have to wrap.
+SomeFunction(
+    {"assume a zero-length name before {"},
+    some_other_function_parameter);
+SomeType variable{
+    some, other, values,
+    {"assume a zero-length name before {"},
+    SomeOtherType{
+        "Very long string requiring the surrounding breaks.",
+        some, other values},
+    SomeOtherType{"Slightly shorter string",
+                  some, other, values}};
+SomeType variable{
+    "This is too long to fit all in one line"};
+MyType m = {  // Here, you could also break before {.
+    superlongvariablename1,
+    superlongvariablename2,
+    {short, interior, list},
+    {interiorwrappinglist,
+     interiorwrappinglist2}};
+
+ +
+ +

Conditionals

+ +
+

Prefer no spaces inside parentheses. The if +and else keywords belong on separate lines.

+
+ +
+ +

There are two acceptable formats for a basic +conditional statement. One includes spaces between the +parentheses and the condition, and one does not.

+ +

The most common form is without spaces. Either is +fine, but be consistent. If you are modifying a +file, use the format that is already present. If you are +writing new code, use the format that the other files in +that directory or project use. If in doubt and you have +no personal preference, do not add the spaces.

+ +
if (condition) {  // no spaces inside parentheses
+  ...  // 2 space indent.
+} else if (...) {  // The else goes on the same line as the closing brace.
+  ...
+} else {
+  ...
+}
+
+ +

If you prefer you may add spaces inside the +parentheses:

+ +
if ( condition ) {  // spaces inside parentheses - rare
+  ...  // 2 space indent.
+} else {  // The else goes on the same line as the closing brace.
+  ...
+}
+
+ +

Note that in all cases you must have a space between +the if and the open parenthesis. You must +also have a space between the close parenthesis and the +curly brace, if you're using one.

+ +
if(condition) {   // Bad - space missing after IF.
+if (condition){   // Bad - space missing before {.
+if(condition){    // Doubly bad.
+
+ +
if (condition) {  // Good - proper space after IF and before {.
+
+ +

Short conditional statements may be written on one +line if this enhances readability. You may use this only +when the line is brief and the statement does not use the +else clause.

+ +
if (x == kFoo) return new Foo();
+if (x == kBar) return new Bar();
+
+ +

This is not allowed when the if statement has an +else:

+ +
// Not allowed - IF statement on one line when there is an ELSE clause
+if (x) DoThis();
+else DoThat();
+
+ +

In general, curly braces are not required for +single-line statements, but they are allowed if you like +them; conditional or loop statements with complex +conditions or statements may be more readable with curly +braces. Some +projects require that an +if must always always have an accompanying +brace.

+ +
if (condition)
+  DoSomething();  // 2 space indent.
+
+if (condition) {
+  DoSomething();  // 2 space indent.
+}
+
+ +

However, if one part of an +if-else statement uses curly +braces, the other part must too:

+ +
// Not allowed - curly on IF but not ELSE
+if (condition) {
+  foo;
+} else
+  bar;
+
+// Not allowed - curly on ELSE but not IF
+if (condition)
+  foo;
+else {
+  bar;
+}
+
+ +
// Curly braces around both IF and ELSE required because
+// one of the clauses used braces.
+if (condition) {
+  foo;
+} else {
+  bar;
+}
+
+ +
+ +

Loops and Switch Statements

+ +
+

Switch statements may use braces for blocks. Annotate +non-trivial fall-through between cases. +Braces are optional for single-statement loops. +Empty loop bodies should use {} or continue.

+
+ +
+ +

case blocks in switch +statements can have curly braces or not, depending on +your preference. If you do include curly braces they +should be placed as shown below.

+ +

If not conditional on an enumerated value, switch +statements should always have a default case +(in the case of an enumerated value, the compiler will +warn you if any values are not handled). If the default +case should never execute, simply +assert:

+ + + +
+
switch (var) {
+  case 0: {  // 2 space indent
+    ...      // 4 space indent
+    break;
+  }
+  case 1: {
+    ...
+    break;
+  }
+  default: {
+    assert(false);
+  }
+}
+
+
+ + + + + +

Braces are optional for single-statement loops.

+ +
for (int i = 0; i < kSomeNumber; ++i)
+  printf("I love you\n");
+
+for (int i = 0; i < kSomeNumber; ++i) {
+  printf("I take it back\n");
+}
+
+ + +

Empty loop bodies should use {} or +continue, but not a single semicolon.

+ +
while (condition) {
+  // Repeat test until it returns false.
+}
+for (int i = 0; i < kSomeNumber; ++i) {}  // Good - empty body.
+while (condition) continue;  // Good - continue indicates no logic.
+
+ +
while (condition);  // Bad - looks like part of do/while loop.
+
+ +
+ +

Pointer and Reference Expressions

+ +
+

No spaces around period or arrow. Pointer operators do not +have trailing spaces.

+
+ +
+ +

The following are examples of correctly-formatted +pointer and reference expressions:

+ +
x = *p;
+p = &x;
+x = r.y;
+x = r->y;
+
+ +

Note that:

+ +
    +
  • There are no spaces around the period or arrow when + accessing a member.
    • + +
  • Pointer operators have no space after the + * or &.
    • +
+ +

When declaring a pointer variable or argument, you may +place the asterisk adjacent to either the type or to the +variable name:

+ +
// These are fine, space preceding.
+char *c;
+const string &str;
+
+// These are fine, space following.
+char* c;    // but remember to do "char* c, *d, *e, ...;"!
+const string& str;
+
+ +
char * c;  // Bad - spaces on both sides of *
+const string & str;  // Bad - spaces on both sides of &
+
+ +

You should do this consistently within a single +file, +so, when modifying an existing file, use the style in +that file.

+ +
+ +

Boolean Expressions

+ +
+

When you have a boolean expression that is longer than the +standard line length, be +consistent in how you break up the lines.

+
+ +
+ +

In this example, the logical AND operator is always at +the end of the lines:

+ +
if (this_one_thing > this_other_thing &&
+    a_third_thing == a_fourth_thing &&
+    yet_another && last_one) {
+  ...
+}
+
+ +

Note that when the code wraps in this example, both of +the && logical AND operators are at +the end of the line. This is more common in Google code, +though wrapping all operators at the beginning of the +line is also allowed. Feel free to insert extra +parentheses judiciously because they can be very helpful +in increasing readability when used +appropriately. Also note that you should always use +the punctuation operators, such as +&& and ~, rather than +the word operators, such as and and +compl.

+ +
+ +

Return Values

+ +
+

Do not needlessly surround the return +expression with parentheses.

+
+ +
+ +

Use parentheses in return expr; only +where you would use them in x = expr;.

+ +
return result;                  // No parentheses in the simple case.
+// Parentheses OK to make a complex expression more readable.
+return (some_long_condition &&
+        another_condition);
+
+ +
return (value);                // You wouldn't write var = (value);
+return(result);                // return is not a function!
+
+ +
+ + + +

Variable and Array Initialization

+ +
+

Your choice of =, (), or +{}.

+
+ +
+ +

You may choose between =, +(), and {}; the following are +all correct:

+ +
int x = 3;
+int x(3);
+int x{3};
+string name = "Some Name";
+string name("Some Name");
+string name{"Some Name"};
+
+ +

Be careful when using a braced initialization list {...} +on a type with an std::initializer_list constructor. +A nonempty braced-init-list prefers the +std::initializer_list constructor whenever +possible. Note that empty braces {} are special, and +will call a default constructor if available. To force the +non-std::initializer_list constructor, use parentheses +instead of braces.

+ +
vector<int> v(100, 1);  // A vector of 100 1s.
+vector<int> v{100, 1};  // A vector of 100, 1.
+
+ +

Also, the brace form prevents narrowing of integral +types. This can prevent some types of programming +errors.

+ +
int pi(3.14);  // OK -- pi == 3.
+int pi{3.14};  // Compile error: narrowing conversion.
+
+ +
+ +

Preprocessor Directives

+ +
+

The hash mark that starts a preprocessor directive should +always be at the beginning of the line.

+
+ +
+ +

Even when preprocessor directives are within the body +of indented code, the directives should start at the +beginning of the line.

+ +
// Good - directives at beginning of line
+  if (lopsided_score) {
+#if DISASTER_PENDING      // Correct -- Starts at beginning of line
+    DropEverything();
+# if NOTIFY               // OK but not required -- Spaces after #
+    NotifyClient();
+# endif
+#endif
+    BackToNormal();
+  }
+
+ +
// Bad - indented directives
+  if (lopsided_score) {
+    #if DISASTER_PENDING  // Wrong!  The "#if" should be at beginning of line
+    DropEverything();
+    #endif                // Wrong!  Do not indent "#endif"
+    BackToNormal();
+  }
+
+ +
+ +

Class Format

+ +
+

Sections in public, protected and +private order, each indented one space.

+
+ +
+ +

The basic format for a class declaration (lacking the +comments, see Class +Comments for a discussion of what comments are +needed) is:

+ +
class MyClass : public OtherClass {
+ public:      // Note the 1 space indent!
+  MyClass();  // Regular 2 space indent.
+  explicit MyClass(int var);
+  ~MyClass() {}
+
+  void SomeFunction();
+  void SomeFunctionThatDoesNothing() {
+  }
+
+  void set_some_var(int var) { some_var_ = var; }
+  int some_var() const { return some_var_; }
+
+ private:
+  bool SomeInternalFunction();
+
+  int some_var_;
+  int some_other_var_;
+};
+
+ +

Things to note:

+ +
    +
  • Any base class name should be on the same line as + the subclass name, subject to the 80-column limit.
    • + +
  • The public:, protected:, + and private: keywords should be indented + one space.
    • + +
  • Except for the first instance, these keywords + should be preceded by a blank line. This rule is + optional in small classes.
    • + +
  • Do not leave a blank line after these + keywords.
    • + +
  • The public section should be first, + followed by the protected and finally the + private section.
    • + +
  • See Declaration + Order for rules on ordering declarations within + each of these sections.
    • +
+ +
+ +

Constructor Initializer Lists

+ +
+

Constructor initializer lists can be all on one line or +with subsequent lines indented four spaces.

+
+ +
+ +

There are two acceptable formats for initializer +lists:

+ +
// When it all fits on one line:
+MyClass::MyClass(int var) : some_var_(var), some_other_var_(var + 1) {}
+
+ +

or

+ +
// When it requires multiple lines, indent 4 spaces, putting the colon on
+// the first initializer line:
+MyClass::MyClass(int var)
+    : some_var_(var),             // 4 space indent
+      some_other_var_(var + 1) {  // lined up
+  ...
+  DoSomething();
+  ...
+}
+
+ +
+ +

Namespace Formatting

+ +
+

The contents of namespaces are not indented.

+
+ +
+ +

Namespaces do not add an +extra level of indentation. For example, use:

+ +
namespace {
+
+void foo() {  // Correct.  No extra indentation within namespace.
+  ...
+}
+
+}  // namespace
+
+ +

Do not indent within a namespace:

+ +
namespace {
+
+  // Wrong.  Indented when it should not be.
+  void foo() {
+    ...
+  }
+
+}  // namespace
+
+ +

When declaring nested namespaces, put each namespace +on its own line.

+ +
namespace foo {
+namespace bar {
+
+ +
+ +

Horizontal Whitespace

+ +
+

Use of horizontal whitespace depends on location. Never put +trailing whitespace at the end of a line.

+
+ +
+ +

General

+ +
void f(bool b) {  // Open braces should always have a space before them.
+  ...
+int i = 0;  // Semicolons usually have no space before them.
+// Spaces inside braces for braced-init-list are optional.  If you use them,
+// put them on both sides!
+int x[] = { 0 };
+int x[] = {0};
+
+// Spaces around the colon in inheritance and initializer lists.
+class Foo : public Bar {
+ public:
+  // For inline function implementations, put spaces between the braces
+  // and the implementation itself.
+  Foo(int b) : Bar(), baz_(b) {}  // No spaces inside empty braces.
+  void Reset() { baz_ = 0; }  // Spaces separating braces from implementation.
+  ...
+
+ +

Adding trailing whitespace can cause extra work for +others editing the same file, when they merge, as can +removing existing trailing whitespace. So: Don't +introduce trailing whitespace. Remove it if you're +already changing that line, or do it in a separate +clean-up +operation (preferably when no-one +else is working on the file).

+ +

Loops and Conditionals

+ +
if (b) {          // Space after the keyword in conditions and loops.
+} else {          // Spaces around else.
+}
+while (test) {}   // There is usually no space inside parentheses.
+switch (i) {
+for (int i = 0; i < 5; ++i) {
+// Loops and conditions may have spaces inside parentheses, but this
+// is rare.  Be consistent.
+switch ( i ) {
+if ( test ) {
+for ( int i = 0; i < 5; ++i ) {
+// For loops always have a space after the semicolon.  They may have a space
+// before the semicolon, but this is rare.
+for ( ; i < 5 ; ++i) {
+  ...
+
+// Range-based for loops always have a space before and after the colon.
+for (auto x : counts) {
+  ...
+}
+switch (i) {
+  case 1:         // No space before colon in a switch case.
+    ...
+  case 2: break;  // Use a space after a colon if there's code after it.
+
+ +

Operators

+ +
// Assignment operators always have spaces around them.
+x = 0;
+
+// Other binary operators usually have spaces around them, but it's
+// OK to remove spaces around factors.  Parentheses should have no
+// internal padding.
+v = w * x + y / z;
+v = w*x + y/z;
+v = w * (x + z);
+
+// No spaces separating unary operators and their arguments.
+x = -5;
+++x;
+if (x && !y)
+  ...
+
+ +

Templates and Casts

+ +
// No spaces inside the angle brackets (< and >), before
+// <, or between >( in a cast
+vector<string> x;
+y = static_cast<char*>(x);
+
+// Spaces between type and pointer are OK, but be consistent.
+vector<char *> x;
+set<list<string>> x;        // Permitted in C++11 code.
+set<list<string> > x;       // C++03 required a space in > >.
+
+// You may optionally use symmetric spacing in < <.
+set< list<string> > x;
+
+ +
+ +

Vertical Whitespace

+ +
+

Minimize use of vertical whitespace.

+
+ +
+ +

This is more a principle than a rule: don't use blank +lines when you don't have to. In particular, don't put +more than one or two blank lines between functions, +resist starting functions with a blank line, don't end +functions with a blank line, and be discriminating with +your use of blank lines inside functions.

+ +

The basic principle is: The more code that fits on one +screen, the easier it is to follow and understand the +control flow of the program. Of course, readability can +suffer from code being too dense as well as too spread +out, so use your judgement. But in general, minimize use +of vertical whitespace.

+ +

Some rules of thumb to help when blank lines may be +useful:

+ +
    +
  • Blank lines at the beginning or end of a function + very rarely help readability.
    • + +
  • Blank lines inside a chain of if-else blocks may + well help readability.
    • +
+ +
+ +

Exceptions to the Rules

+ +

The coding conventions described above are mandatory. +However, like all good rules, these sometimes have exceptions, +which we discuss here.

+ + + +
+

Existing Non-conformant Code

+ +
+

You may diverge from the rules when dealing with code that +does not conform to this style guide.

+
+ +
+ +

If you find yourself modifying code that was written +to specifications other than those presented by this +guide, you may have to diverge from these rules in order +to stay consistent with the local conventions in that +code. If you are in doubt about how to do this, ask the +original author or the person currently responsible for +the code. Remember that consistency includes +local consistency, too.

+ +
+
+ + +

Parting Words

+ +

Use common sense and BE CONSISTENT.

+ +

If you are editing code, take a few minutes to look at the +code around you and determine its style. If they use spaces +around their if clauses, you should, too. If their +comments have little boxes of stars around them, make your +comments have little boxes of stars around them too.

+ +

The point of having style guidelines is to have a common +vocabulary of coding so people can concentrate on what you are +saying, rather than on how you are saying it. We present global +style rules here so people know the vocabulary. But local style +is also important. If code you add to a file looks drastically +different from the existing code around it, the discontinuity +throws readers out of their rhythm when they go to read it. Try +to avoid this.

+ + + +

OK, enough writing about writing code; the code itself is much +more interesting. Have fun!

+ +
+ +

Revision 4.45

+ +
+ diff --git a/styleguide/eclipse-cpp-google-style.xml b/styleguide/eclipse-cpp-google-style.xml new file mode 100644 index 0000000000..aa05a819ab --- /dev/null +++ b/styleguide/eclipse-cpp-google-style.xml @@ -0,0 +1,167 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/styleguide/eclipse-java-google-style.xml b/styleguide/eclipse-java-google-style.xml new file mode 100644 index 0000000000..b3177d30f3 --- /dev/null +++ b/styleguide/eclipse-java-google-style.xml @@ -0,0 +1,337 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/styleguide/include/link.png b/styleguide/include/link.png new file mode 100644 index 0000000000000000000000000000000000000000..75d5c7ba8dcc22b100b18b8c800da9ed99afbf7b GIT binary patch literal 189 zcmeAS@N?(olHy`uVBq!ia0vp^q9Dw{1|(OCFP#RYT0C7GLo80eoovW;K!L}#nDP3f zLaS;${>#Z0UFCva2M?aC%WS)H?QB_5g+S7$o~{tDg%>YO@zZ2dVrDwAKuzez0i`Ul zbE@l3-bt1V61%3rbUmT<%Dy%3?@ZTjdAE&Ol|^ce?3NY5cci0UGX8nXab09-b9Pp3 o=^vw)Kdk>g`TD$n)}_KZpTAr6giAPD0^P&l>FVdQ&MBb@0Ar|2 lowestLevel) continue; + + // If level is a masterLevel, make it a TOC parent category + if ((level == masterLevel) && (!hasClass(heading, 'ignoreLink'))) { + toc_current_row = AddTOCMaster(tbody_element, heading); + ignoreChildren = false; + } + + if ((level == masterLevel) && (hasClass(heading, 'ignoreLink'))) { + ignoreChildren = true; + } + + if ((level != masterLevel) && (!ignoreChildren)) { + AddTOCElements(toc_current_row, heading); + } + + // Advance the header counter + h++; + } +} + +// Adds a master Table of Content heading +function AddTOCMaster(tocTable, heading) { + + // Add the table row scaffolding + var toc_tr = document.createElement('tr'); + tocTable.appendChild(toc_tr); + toc_tr.setAttribute('valign', 'top'); + var toc_tr_td = document.createElement('td'); + toc_tr.appendChild(toc_tr_td); + var toc_category = document.createElement('div'); + toc_tr_td.appendChild(toc_category); + toc_category.className = 'toc_category'; + + // Create the link to this header + var link = document.createElement('a'); + link.href = '#' + heading.id; // Create the anchor link + link.textContent = heading.textContent; // Link text is same as heading + toc_category.appendChild(link); + + // Add the container table cell for its children + var toc_td = document.createElement('td'); + toc_tr.appendChild(toc_td); + var toc_td_div = document.createElement('div'); + toc_td_div.className = 'toc_stylepoint'; + toc_td.appendChild(toc_td_div); + + return (toc_td_div); +} + +// Adds Table of Contents element to a master heading as children +function AddTOCElements(toc_div, heading) { + + if (heading.offsetParent === null) { + // The element is currently hidden, so don't create a TOC entry + } else { + // Create the list item element + var toc_list_element = document.createElement('li'); + toc_list_element.className = 'toc_entry'; + toc_div.appendChild(toc_list_element); + + // Create the link to this header + var link = document.createElement('a'); + link.href = '#' + heading.id; // Create the anchor link + link.textContent = heading.textContent; // Link text is same as heading + toc_list_element.appendChild(link); + } +} + +function CreateVerticalTOC(headings, masterLevel, lowestLevel, tbody_element) { + + // Create the Column scaffolding + var toc_tr = document.createElement('tr'); + tbody_element.appendChild(toc_tr); + var toc_tr_td = document.createElement('td'); + toc_tr_td.className = 'two_columns'; + toc_tr.appendChild(toc_tr_td); + + + // Initialize the header counter and the current row + var h = 0; + var toc_current_col = null; + var ignoreChildren = false; + + while (h < headings.length) { + // Get current heading + var heading = headings[h]; + + // Get the current heading level + var level = parseInt(heading.tagName.charAt(1)); + + if (isNaN(level) || level < 1 || level > lowestLevel) continue; + + // If level is a masterLevel, make it a TOC parent category + if ((level == masterLevel) && (!hasClass(heading, 'ignoreLink'))) { + if (heading.offsetParent === null) { + // The element is currently hidden, so don't create a TOC entry + } else { + var td_dl = document.createElement('dl'); + toc_tr_td.appendChild(td_dl); + var td_dt = document.createElement('dt'); + td_dl.appendChild(td_dt); + toc_current_col = td_dl; + + // Create the link to this header + var link = document.createElement('a'); + link.href = '#' + heading.id; // Create the anchor link + link.textContent = heading.textContent; // Link text is same as heading + td_dt.appendChild(link); + ignoreChildren = false; + } + } + + // If level is a masterLevel but it's specified to ignore links, skip it + // and its children. + if ((level == masterLevel) && (hasClass(heading, 'ignoreLink'))) { + ignoreChildren = true; + } + + if ((level != masterLevel) && (!ignoreChildren)) { + if (heading.offsetParent === null) { + // The element is currently hidden, so don't create a TOC entry + } else { + var td_dd = document.createElement('dd'); + toc_current_col.appendChild(td_dd); + // Create the link to this header + var link = document.createElement('a'); + link.href = '#' + heading.id; // Create the anchor link + link.textContent = heading.textContent; // Link text is same as heading + td_dd.appendChild(link); + } + } + + // Advance the header counter + h++; + } +} + +/* + * Utility function for finding elements with a given + * class. + */ +function hasClass(element, cls) { + return (' ' + element.className + ' ').indexOf(' ' + cls + ' ') > -1; +} + +/* + * Linkify all h2 through h4 headers, except for those marked + * "ignoreLink" + */ + +// Add the link image to the element. +function LinkifyHeader(header, fileName, sizePixels) { + var link = document.createElement('a'); + link.href = '#' + header.id; + link.alt = 'link to ' + header.id; + link.innerHTML = + ''; + header.appendChild(link); +} + +// Find all elements of the given tag and linkify if +// they don't have 'ignoreLink' in their class. +function LinkifyHeadersForTag(tagName) { + var headers = document.getElementsByTagName(tagName); + var header; + for (var j = 0; j != headers.length; j++) { + header = headers[j]; + if (!hasClass(header, 'ignoreLink') && ('id' in header)) { + if (header.id != '') { + LinkifyHeader(header, 'link.png', 21); + header.style.left = '-46px'; + header.style.position = 'relative'; + } + } + } +} + +// Linkify all h2, h3, and h4s. h1s are titles. +function LinkifyHeaders() { + LinkifyHeadersForTag('h2'); + LinkifyHeadersForTag('h3'); + LinkifyHeadersForTag('h4'); +} + +/* + * Initialize the style guide by showing all internal + * elements and then linkifying the headers. + */ + +function initStyleGuide() { + LinkifyHeaders(); + CreateTOC('tocDiv'); +} diff --git a/styleguide/javaguide.css b/styleguide/javaguide.css new file mode 100644 index 0000000000..c42ba835a0 --- /dev/null +++ b/styleguide/javaguide.css @@ -0,0 +1,515 @@ +table { + border-collapse: collapse; +} + +td, th { + border: 1px solid #ccc; + padding: 2px 12px; + font-size: 10pt; +} + +code, samp, var { + color: #060; +} + +pre { + font-size: 10pt; + display: block; + color: #060; + background-color: #e8fff6; + border-color: #f0fff0; + border-style: solid; + border-top-width: 1px; + border-bottom-width: 1px; + border-right-width: 1px; + border-left-width: 5px; + padding-left: 12px; + padding-right: 12px; + padding-top: 4px; + padding-bottom: 4px; +} + +pre.badcode { + color: #c00; + background-color: #ffe6d8; + border-color: #fff0f0; +} + +hr { + margin-top: 3.5em; + border-width: 1px; + color: #fff; +} + +html { + margin-top:2em; + margin-left:10%; + margin-right:10%; + padding:0; +} + +.bp-reset-element, +body, +h1, +h2, +h3, +h4, +h5, +h6, +article, +aside, +details, +figcaption, +figure, +footer, +header, +hgroup, +menu, +nav, +section, +summary, +blockquote, +q, +th, +td, +caption, +table, +div, +span, +object, +iframe, +p, +pre, +a, +abbr, +acronym, +address, +code, +del, +dfn, +em, +img, +dl, +dt, +dd, +ol, +ul, +li, +fieldset, +form, +label, +legend, +caption, +tbody, +tfoot, +thead, +tr { + margin:0; + padding:0; + border:0; + font-weight:inherit; + font-style:inherit; + font-size:100%; + font-family:inherit; + vertical-align:baseline; +} + +body { + font-family:'Arial', sans-serif; + font-size:81.25%; + color:#222; + background-color:#fff; + line-height:1.67; + overflow: auto; +} + +.change { + text-align: right; + margin-bottom:1em; +} + +em { + font-style: italic +} + +h1, +h2, +h3, +h4, +h5, +h6 { + font-weight:bold; +} + +h1 { + margin-bottom:.50em; + text-align: center +} + +h2, +h3, +h4, +h5, +h6 { + margin-top:1.5em; + margin-bottom:.75em; +} + +h1 {font-size:200%;} +h2 {font-size:167%;} +h3 {font-size:133%;} +h4 {font-size:120%;} +h5 {font-size:110%;} + +p { + margin:0 0 1.5em; +} + +a[href=''] { + cursor:default; +} + +h1 img, +h2 img, +h3 img, +h4 img, +h5 img, +h6 img { + margin:0; +} + +a img { + border:none; +} + +pre { + margin:1.5em 0; + white-space:pre; +} + +pre, +code, +kbd, +tt { + font:1em 'Droid Sans Mono', monospace; + line-height:1.5; +} + +dl { + margin:0 0 1.5em 0; +} + +dl dt { + font-weight:bold; +} + +dd { + margin-left:1.5em; +} + +dd.toc3 { + margin-left:3em; +} + +hr { + height:0; + border:0; + border-top:1px solid #ccc; + background-color:#ccc; +} + +table { + border:1px solid #bbb; + border-spacing:0; + border-collapse:collapse; + margin:0 0 1.5em; + vertical-align:middle; + width:100%; +} + +table.unlined, +table.unlined th, +table.unlined tr, +table.unlined td { + border:0; +} + +th, +td, +caption { + float:none !important; + text-align:left; + font-weight:normal; + vertical-align:middle; + padding:4px; +} + +caption { + padding:0; +} + +td { + border:1px solid #bbb; + vertical-align:top; +} + +th { + border:0; + border-bottom:1px solid black; + font-weight:bold; + background:rgb(229, 236, 249); +} + +table th code { + background-color:inherit; + color:inherit; +} + +table tfoot th { + border:1px solid #bbb; +} + +tfoot { + font-style:italic; +} + +caption { + background:#eee; +} + +table[border='0'] { + border:none; +} + +table[border='0']>tbody>tr>td, +table[border='0']>tr>td { + border:none; +} + +tr.alt td, +td.alt { + background-color:#efefef; +} + +table.striped tr:nth-child(even) td, +table tr.even td { + background:#efefef; +} + +table.columns { + border:none; +} + +table.columns>tbody>tr>td, +table.columns>tr>td { + border:none; + padding:0 3em 0 0; +} + +table.columns>tbody>tr>td:last-child, +table.columns>tr>td:last-child { + border:none; + padding:0; +} + +ul, +ol { + margin:0 1.5em 1.5em 0; + padding-left:2em; +} + +li ul, +li ol { + margin:0; +} + +ul { + list-style-type:disc; +} + +ol { + list-style-type:decimal; +} + +ul { + list-style-type:disc; +} + +ul ul { + list-style-type:circle; +} + +ul ul ul { + list-style-type:square; +} + +ul.disc { + list-style-type:disc; +} + +ul.circle { + list-style-type:circle; +} + +ul.square { + list-style-type:square; +} + +ol { + list-style-type:decimal; +} + +ol ol { + list-style-type:lower-alpha; +} + +ol ol ol { + list-style-type:lower-roman; +} + +ol ul { + list-style-type:circle; +} + +ol.decimal { + list-style-type:decimal; +} + +ol.upper-alpha { + list-style-type:upper-alpha; +} + +ol.lower-alpha { + list-style-type:lower-alpha; +} + +ol.upper-roman { + list-style-type:upper-roman; +} + +ol.lower-roman { + list-style-type:lower-roman; +} + +ol.nolist, +ul.nolist { + padding-left:0; + list-style-image:none; + list-style-type:none; + margin-left:0; +} + +.center { + text-align:center; +} + +code, +kbd, +pre { + color:#009900; +} + +kbd { + font-weight: bold; +} + +table.striped code { + background-color:inherit; +} + +pre { + padding:6px 10px; + background-color:#FAFAFA; + border:1px solid #bbb; + overflow:auto; +} + +pre.prettyprint { + padding:6px 10px !important; + border:1px solid #bbb !important; +} + +code.bad, code.badcode { + color: magenta; +} +pre.bad, pre.badcode { + background-color:#ffe6d8; + border-top:1px inset #a03; + border-left:1px inset #a03; +} + +.tip { + background-color:#fffbd9; + padding:6px 8px 6px 10px; + border-left:6px solid #ffef70; +} + +.note { + background-color:#e5ecf9; + padding:6px 8px 6px 10px; + border-left:6px solid #36c; +} + +@media print { + + .str { + color:#060; + } + + .kwd { + color:#006; + font-weight:bold; + } + + .com { + color:#600; + font-style:italic; + } + + .typ { + color:#404; + font-weight:bold; + } + + .lit { + color:#044; + } + + .pun, + .opn, + .clo { + color:#440; + } + + .pln { + color:#000; + } + + .tag { + color:#006; + font-weight:bold; + } + + .atn { + color:#404; + } + + .atv { + color:#060; + } + + h1 { + font-style:italic; + } +} + +ol.linenums { + margin-top:0; + margin-bottom:0; +} + +code { + background-color:#FAFAFA; + padding: 0.25em 0.5em; + white-space: nowrap +} diff --git a/styleguide/javaguide.html b/styleguide/javaguide.html new file mode 100644 index 0000000000..da34b8516b --- /dev/null +++ b/styleguide/javaguide.html @@ -0,0 +1,806 @@ + + + + + + + WPILib Java Style + + +

WPILib Java Style (Based on the + Google Java Style Guide)

+
Last changed: June 19, 2015
+ + + + +
+
+
+
+1 Introduction +
+
+1.1 Terminology notes +
+
+1.2 Guide notes +
+
+
+2 Source file basics +
+
+2.1 File name +
+
+2.2 File encoding: UTF-8 +
+
+2.3 Special characters +
+
+2.3.1 Whitespace characters +
+
+2.3.2 Special escape sequences +
+
+2.3.3 Non-ASCII characters +
+
+
+3 Source file structure +
+
+3.1 License or copyright information, if present +
+
+3.2 Package statement +
+
+3.3 Import statements +
+
+3.3.1 No wildcard imports +
+
+3.3.2 No line-wrapping +
+
+3.3.3 Ordering and spacing +
+
+3.4 Class declaration +
+
+3.4.1 Exactly one top-level class declaration +
+
+3.4.2 Class member ordering +
+
+		 +
+
+
+4 Formatting +
+
+4.1 Braces +
+
+4.1.1 Braces are used where optional +
+
+4.1.2 Nonempty blocks: K & R style +
+
+4.1.3 Empty blocks: may be concise +
+
+4.2 Block indentation: +2 spaces +
+
+4.3 One statement per line +
+
+4.4 Column limit: 80 or 100 +
+
+4.5 Line-wrapping +
+
+4.5.1 Where to break +
+
+4.5.2 Indent continuation lines at least +4 spaces +
+
+4.6 Whitespace +
+
+4.6.1 Vertical Whitespace +
+
+4.6.2 Horizontal whitespace +
+
+4.6.3 Horizontal alignment: never required +
+
+4.7 Grouping parentheses: recommended +
+
+4.8 Specific constructs +
+
+4.8.1 Enum classes +
+
+4.8.2 Variable declarations +
+
+4.8.3 Arrays +
+
+4.8.4 Switch statements +
+
+4.8.5 Annotations +
+
+4.8.6 Comments +
+
+4.8.7 Modifiers +
+
+4.8.8 Numeric Literals +
+
+		 +
+
+
+5 Naming +
+
+5.1 Rules common to all identifiers +
+
+5.2 Rules by identifier type +
+
+5.2.1 Package names +
+
+5.2.2 Class names +
+
+5.2.3 Method names +
+
+5.2.4 Constant names +
+
+5.2.5 Non-constant field names +
+
+5.2.6 Parameter names +
+
+5.2.7 Local variable names +
+
+5.2.8 Type variable names +
+
+5.3 Camel case: defined +
+
+
+6 Programming Practices +
+
+6.1 @Override: always used +
+
+6.2 Caught exceptions: not ignored +
+
+6.3 Static members: qualified using class +
+
+6.4 Finalizers: not used +
+
+
+7 Javadoc +
+
+7.1 Formatting +
+
+7.1.1 General form +
+
+7.1.2 Paragraphs +
+
+7.1.3 At-clauses +
+
+7.2 The summary fragment +
+
+7.3 Where Javadoc is used +
+
+7.3.1 Exception: self-explanatory methods +
+
+7.3.2 Exception: overrides +
+
+
+
+

1 Introduction 

+ +

This guide is a work in progress. +We are currently working on getting this guide updated to +a point where it is useful for WPILib developers to use.

+ +

This document serves as the style guide for WPILib. It is heavily + based on the Google Java Style Guide and copies pretty much word-for-word + the formatting/style components of the guide while cutting a couple + of the programming practices. As this guide evolves, we will likely + introduce more suggested/mandated programming practices specific + to WPILib.

+

It is encouraged that anyone working on the Java WPILib also + read the corresponding C++ guide, as we generally try to develop + the C++ and Java components of the library in parallel and many + programming practices true in one language will be true in the other + (although this is not universally true).

+

+

1.1 Terminology notes 

+

In this document, unless otherwise clarified:

  1. The term class is used inclusively to mean an "ordinary" class, enum class, + interface or annotation type (@interface).
  2. The term comment always refers to implementation comments. We do not + use the phrase "documentation comments", instead using the common term "Javadoc."

Other "terminology notes" will appear occasionally throughout the document.

+

1.2 Guide notes 

+

Example code in this document is non-normative. That is, while the examples +are in Google Style, they may not illustrate the only stylish way to represent the +code. Optional formatting choices made in examples should not be enforced as rules.

+

2 Source file basics 

+ +

2.1 File name 

+

The source file name consists of the case-sensitive name of the top-level class it contains, +plus the .java extension.

+

2.2 File encoding: UTF-8 

+

Source files are encoded in UTF-8.

+

2.3 Special characters 

+ +

2.3.1 Whitespace characters 

+

Aside from the line terminator sequence, the ASCII horizontal space +character (0x20) is the only whitespace character that appears +anywhere in a source file. This implies that:

  1. All other whitespace characters in string and character literals are escaped.
  2. Tab characters are not used for indentation.
+

2.3.2 Special escape sequences 

+

For any character that has a special escape sequence +(\b, +\t, +\n, +\f, +\r, +\", +\' and +\\), that sequence +is used rather than the corresponding octal +(e.g. \012) or Unicode +(e.g. \u000a) escape.

+

2.3.3 Non-ASCII characters 

+

For the remaining non-ASCII characters, either the actual Unicode character +(e.g. ∞) or the equivalent Unicode escape +(e.g. \u221e) is used, depending only on which +makes the code easier to read and understand.

Tip: In the Unicode escape case, and occasionally even when actual +Unicode characters are used, an explanatory comment can be very helpful.

Examples:

ExampleDiscussion
String unitAbbrev = "μs";Best: perfectly clear even without a comment.
String unitAbbrev = "\u03bcs"; // "μs"Allowed, but there's no reason to do this.
String unitAbbrev = "\u03bcs"; + // Greek letter mu, "s"Allowed, but awkward and prone to mistakes.
String unitAbbrev = "\u03bcs";Poor: the reader has no idea what this is.
return '\ufeff' + content; + // byte order markGood: use escapes for non-printable characters, and comment if necessary.

Tip: Never make your code less readable simply out of fear that +some programs might not handle non-ASCII characters properly. If that should happen, those +programs are broken and they must be fixed.

+

3 Source file structure 

+

A source file consists of, in order:

  1. License or copyright information, if present
  2. Package statement
  3. Import statements
  4. Exactly one top-level class

Exactly one blank line separates each section that is present.

+

3.1 License or copyright information, if present 

+

If license or copyright information belongs in a file, it belongs here.

+

3.2 Package statement 

+

The package statement is not line-wrapped. The column limit (Section 4.4, +Column limit: 80) does not apply to package statements.

+

3.3 Import statements 

+ +

3.3.1 No wildcard imports 

+

Wildcard imports, static or otherwise, are not used.

+

3.3.2 No line-wrapping 

+

Import statements are not line-wrapped. The column limit (Section 4.4, +Column limit: 80) does not apply to import +statements.

+

3.3.3 Ordering and spacing 

+

Import statements are divided into the following groups, in this order, with each group +separated by a single blank line:

  1. All static imports in a single group
  2. com.google imports + (only if this source file is in the com.google package + space)
  3. Third-party imports, one group per top-level package, in ASCII sort order +
    • for example: android, com, junit, org, + sun
  4. java imports
  5. javax imports

Within a group there are no blank lines, and the imported names appear in ASCII sort +order. (Note: this is not the same as the import statements being in +ASCII sort order; the presence of semicolons warps the result.)

+

3.4 Class declaration 

+ +

3.4.1 Exactly one top-level class declaration 

+

Each top-level class resides in a source file of its own.

+

3.4.2 Class member ordering 

+

The ordering of the members of a class can have a great effect on learnability, but there is +no single correct recipe for how to do it. Different classes may order their members +differently.

What is important is that each class order its members in some logical +order, which its maintainer could explain if asked. For example, new methods are not +just habitually added to the end of the class, as that would yield "chronological by date +added" ordering, which is not a logical ordering.

+
3.4.2.1 Overloads: never split 
+

When a class has multiple constructors, or multiple methods with the same name, these appear +sequentially, with no intervening members.

+

4 Formatting 

+

Terminology Note: block-like construct refers to +the body of a class, method or constructor. Note that, by Section 4.8.3.1 on +array initializers, any array initializer +may optionally be treated as if it were a block-like construct.

+

4.1 Braces 

+ +

4.1.1 Braces are used where optional 

+

Braces are used with +if, +else, +for, +do and +while statements, even when the +body is empty or contains only a single statement.

+

4.1.2 Nonempty blocks: K & R style 

+

Braces follow the Kernighan and Ritchie style +("Egyptian brackets") +for nonempty blocks and block-like constructs:

  • No line break before the opening brace.
  • Line break after the opening brace.
  • Line break before the closing brace.
  • Line break after the closing brace if that brace terminates a statement or the body + of a method, constructor or named class. For example, there is no line break + after the brace if it is followed by else or a + comma.

Example:

+return new MyClass() {
+  @Override public void method() {
+    if (condition()) {
+      try {
+        something();
+      } catch (ProblemException e) {
+        recover();
+      }
+    }
+  }
+};
+

A few exceptions for enum classes are given in Section 4.8.1, +Enum classes.

+

4.1.3 Empty blocks: may be concise 

+

An empty block or block-like construct may be closed immediately after it is +opened, with no characters or line break in between +({}), unless it is part of a +multi-block statement (one that directly contains multiple blocks: +if/else-if/else or +try/catch/finally).

Example:

+  void doNothing() {}
+
+

4.2 Block indentation: +2 spaces 

+

Each time a new block or block-like construct is opened, the indent increases by two +spaces. When the block ends, the indent returns to the previous indent level. The indent level +applies to both code and comments throughout the block. (See the example in Section 4.1.2, +Nonempty blocks: K & R Style.)

+

4.3 One statement per line 

+

Each statement is followed by a line-break.

+

4.4 Column limit: 80 

+

+ Projects should have a column limit of 80 characters. + +Except as noted below, any line that would exceed this limit must be line-wrapped, as explained in +Section 4.5, Line-wrapping. +

Exceptions:

  1. Lines where obeying the column limit is not possible (for example, a long URL in Javadoc, + or a long JSNI method reference).
  2. package and + import statements (see Sections + 3.2 Package statement and + 3.3 Import statements).
  3. Command lines in a comment that may be cut-and-pasted into a shell.
+

4.5 Line-wrapping 

+

Terminology Note: When code that might otherwise legally +occupy a single line is divided into multiple lines, typically to avoid overflowing the column +limit, this activity is called +line-wrapping.

There is no comprehensive, deterministic formula showing exactly how to line-wrap in +every situation. Very often there are several valid ways to line-wrap the same piece of code.

Tip: Extracting a method or local variable may solve the problem +without the need to line-wrap.

+

4.5.1 Where to break 

+

The prime directive of line-wrapping is: prefer to break at a +higher syntactic level. Also:

  1. When a line is broken at a non-assignment operator the break comes before + the symbol. (Note that this is not the same practice used in Google style for other languages, + such as C++ and JavaScript.) +
    • This also applies to the following "operator-like" symbols: the dot separator + (.), the ampersand in type bounds + (<T extends Foo & Bar>), and the pipe in + catch blocks + (catch (FooException | BarException e)).
  2. When a line is broken at an assignment operator the break typically comes + after the symbol, but either way is acceptable. +
    • This also applies to the "assignment-operator-like" colon in an enhanced + for ("foreach") statement.
  3. A method or constructor name stays attached to the open parenthesis + (() that follows it.
  4. A comma (,) stays attached to the token that + precedes it.
+

4.5.2 Indent continuation lines at least +4 spaces 

+

When line-wrapping, each line after the first (each continuation line) is indented +at least +4 from the original line.

When there are multiple continuation lines, indentation may be varied beyond +4 as +desired. In general, two continuation lines use the same indentation level if and only if they +begin with syntactically parallel elements.

Section 4.6.3 on Horizontal alignment addresses +the discouraged practice of using a variable number of spaces to align certain tokens with +previous lines.

+

4.6 Whitespace 

+ +

4.6.1 Vertical Whitespace 

+

A single blank line appears:

  1. Between consecutive members (or initializers) of a class: fields, constructors, + methods, nested classes, static initializers, instance initializers. +
    • Exception: A blank line between two consecutive + fields (having no other code between them) is optional. Such blank lines are used as needed to + create logical groupings of fields.
  2. Within method bodies, as needed to create logical groupings of statements.
  3. Optionally before the first member or after the last member of the class (neither + encouraged nor discouraged).
  4. As required by other sections of this document (such as Section 3.3, + Import statements).

Multiple consecutive blank lines are permitted, but never required (or encouraged).

+

4.6.2 Horizontal whitespace 

+

Beyond where required by the language or other style rules, and apart from literals, comments and +Javadoc, a single ASCII space also appears in the following places only.

  1. Separating any reserved word, such as + if, + for or + catch, from an open parenthesis + (() + that follows it on that line
  2. Separating any reserved word, such as + else or + catch, from a closing curly brace + (}) that precedes it on that line
  3. Before any open curly brace + ({), with two exceptions: +
    • @SomeAnnotation({a, b}) (no space is used)
    • String[][] x = {{"foo"}}; (no space is required + between {{, by item 8 below)
  4. On both sides of any binary or ternary operator. This also applies to the following + "operator-like" symbols: +
    • the ampersand in a conjunctive type bound: + <T extends Foo & Bar>
    • the pipe for a catch block that handles multiple exceptions: + catch (FooException | BarException e)
    • the colon (:) in an enhanced + for ("foreach") statement
  5. After ,:; or the closing parenthesis + ()) of a cast
  6. On both sides of the double slash (//) that + begins an end-of-line comment. Here, multiple spaces are allowed, but not required.
  7. Between the type and variable of a declaration: + List<String> list
  8. Optional just inside both braces of an array initializer +
    • new int[] {5, 6} and + new int[] { 5, 6 } are both valid

Note: This rule never requires or forbids additional space at the +start or end of a line, only interior space.

+

4.6.3 Horizontal alignment: never required 

+

Terminology Note: Horizontal alignment is the +practice of adding a variable number of additional spaces in your code with the goal of making +certain tokens appear directly below certain other tokens on previous lines.

This practice is permitted, but is never required by Google Style. It is not +even required to maintain horizontal alignment in places where it was already used.

Here is an example without alignment, then using alignment:

+private int x; // this is fine
+private Color color; // this too
+
+private int   x;      // permitted, but future edits
+private Color color;  // may leave it unaligned
+

Tip: Alignment can aid readability, but it creates problems for +future maintenance. Consider a future change that needs to touch just one line. This change may +leave the formerly-pleasing formatting mangled, and that is allowed. More often +it prompts the coder (perhaps you) to adjust whitespace on nearby lines as well, possibly +triggering a cascading series of reformattings. That one-line change now has a "blast radius." +This can at worst result in pointless busywork, but at best it still corrupts version history +information, slows down reviewers and exacerbates merge conflicts.

+

4.7 Grouping parentheses: recommended 

+

Optional grouping parentheses are omitted only when author and reviewer agree that there is no +reasonable chance the code will be misinterpreted without them, nor would they have made the code +easier to read. It is not reasonable to assume that every reader has the entire Java +operator precedence table memorized.

+

4.8 Specific constructs 

+ +

4.8.1 Enum classes 

+

After each comma that follows an enum constant, a line-break is optional.

An enum class with no methods and no documentation on its constants may optionally be formatted +as if it were an array initializer (see Section 4.8.3.1 on +array initializers).

+private enum Suit { CLUBS, HEARTS, SPADES, DIAMONDS }
+

Since enum classes are classes, all other rules for formatting classes apply.

+

4.8.2 Variable declarations 

+ +
4.8.2.1 One variable per declaration 
+

Every variable declaration (field or local) declares only one variable: declarations such as +int a, b; are not used.

+
4.8.2.2 Declared when needed, initialized as soon as +possible 
+

Local variables are not habitually declared at the start of their containing +block or block-like construct. Instead, local variables are declared close to the point they are +first used (within reason), to minimize their scope. Local variable declarations typically have +initializers, or are initialized immediately after declaration.

+

4.8.3 Arrays 

+ +
4.8.3.1 Array initializers: can be "block-like" 
+

Any array initializer may optionally be formatted as if it were a "block-like +construct." For example, the following are all valid (not an exhaustive +list):

+new int[] {           new int[] {
+  0, 1, 2, 3            0,
+}                       1,
+                        2,
+new int[] {             3,
+  0, 1,               }
+  2, 3
+}                     new int[]
+                          {0, 1, 2, 3}
+
+
4.8.3.2 No C-style array declarations 
+

The square brackets form a part of the type, not the variable: +String[] args, not +String args[].

+

4.8.4 Switch statements 

+

Terminology Note: Inside the braces of a +switch block are one or more statement groups. Each statement group consists of +one or more switch labels (either case FOO: or +default:), followed by one or more statements.

+
4.8.4.1 Indentation 
+

As with any other block, the contents of a switch block are indented +2.

After a switch label, a newline appears, and the indentation level is increased +2, exactly as +if a block were being opened. The following switch label returns to the previous indentation +level, as if a block had been closed.

+
4.8.4.2 Fall-through: commented 
+

Within a switch block, each statement group either terminates abruptly (with a +break, +continue, +return or thrown exception), or is marked with a comment +to indicate that execution will or might continue into the next statement group. Any +comment that communicates the idea of fall-through is sufficient (typically +// fall through). This special comment is not required in +the last statement group of the switch block. Example:

+switch (input) {
+  case 1:
+  case 2:
+    prepareOneOrTwo();
+    // fall through
+  case 3:
+    handleOneTwoOrThree();
+    break;
+  default:
+    handleLargeNumber(input);
+}
+
+
4.8.4.3 The default case is present 
+

Each switch statement includes a default statement +group, even if it contains no code.

+

4.8.5 Annotations 

+

Annotations applying to a class, method or constructor appear immediately after the +documentation block, and each annotation is listed on a line of its own (that is, one annotation +per line). These line breaks do not constitute line-wrapping (Section +4.5, Line-wrapping), so the indentation level is not +increased. Example:

+@Override
+@Nullable
+public String getNameIfPresent() { ... }
+

Exception: A single parameterless annotation +may instead appear together with the first line of the signature, for example:

+@Override public int hashCode() { ... }
+

Annotations applying to a field also appear immediately after the documentation block, but in +this case, multiple annotations (possibly parameterized) may be listed on the same line; +for example:

+@Partial @Mock DataLoader loader;
+

There are no specific rules for formatting parameter and local variable annotations.

+

4.8.6 Comments 

+ +
4.8.6.1 Block comment style 
+

Block comments are indented at the same level as the surrounding code. They may be in +/* ... */ style or +// ... style. For multi-line +/* ... */ comments, subsequent lines must start with +* aligned with the * on the previous line.

+/*
+ * This is          // And so           /* Or you can
+ * okay.            // is this.          * even do this. */
+ */
+

Comments are not enclosed in boxes drawn with asterisks or other characters.

Tip: When writing multi-line comments, use the +/* ... */ style if you want automatic code formatters to +re-wrap the lines when necessary (paragraph-style). Most formatters don't re-wrap lines in +// ... style comment blocks.

+

4.8.7 Modifiers 

+

Class and member modifiers, when present, appear in the order +recommended by the Java Language Specification: +

+public protected private abstract static final transient volatile synchronized native strictfp
+
+

4.8.8 Numeric Literals 

+

long-valued integer literals use an uppercase L suffix, never +lowercase (to avoid confusion with the digit 1). For example, 3000000000L +rather than 3000000000l.

+

5 Naming 

+ +

5.1 Rules common to all identifiers 

+

Identifiers use only ASCII letters and digits, and in two cases noted below, underscores. Thus +each valid identifier name is matched by the regular expression \w+ .

In Google Style special prefixes or +suffixes, like those seen in the examples name_, +mName, s_name and +kName, are not used. +For WPILib, we do make one exception to this rule for non-constant field name.

+

5.2 Rules by identifier type 

+ +

5.2.1 Package names 

+

Package names are all lowercase, with consecutive words simply concatenated together (no +underscores). For example, com.example.deepspace, not +com.example.deepSpace or +com.example.deep_space.

+

5.2.2 Class names 

+

Class names are written in UpperCamelCase.

Class names are typically nouns or noun phrases. For example, +Character or +ImmutableList. Interface names may also be nouns or +noun phrases (for example, List), but may sometimes be +adjectives or adjective phrases instead (for example, +Readable).

There are no specific rules or even well-established conventions for naming annotation types.

Test classes are named starting with the name of the class they are testing, and ending +with Test. For example, +HashTest or +HashIntegrationTest.

+

5.2.3 Method names 

+

Method names are written in lowerCamelCase.

Method names are typically verbs or verb phrases. For example, +sendMessage or +stop.

Underscores may appear in JUnit test method names to separate logical components of the +name. One typical pattern is test<MethodUnderTest>_<state>, +for example testPop_emptyStack. There is no One Correct +Way to name test methods.

+

5.2.4 Constant names 

+

Constant names use CONSTANT_CASE: all uppercase +letters, with words separated by underscores. But what is a constant, exactly?

Every constant is a static final field, but not all static final fields are constants. Before +choosing constant case, consider whether the field really feels like a constant. For +example, if any of that instance's observable state can change, it is almost certainly not a +constant. Merely intending to never mutate the object is generally not +enough. Examples:

+// Constants
+static final int NUMBER = 5;
+static final ImmutableList<String> NAMES = ImmutableList.of("Ed", "Ann");
+static final Joiner COMMA_JOINER = Joiner.on(',');  // because Joiner is immutable
+static final SomeMutableType[] EMPTY_ARRAY = {};
+enum SomeEnum { ENUM_CONSTANT }
+
+// Not constants
+static String nonFinal = "non-final";
+final String nonStatic = "non-static";
+static final Set<String> mutableCollection = new HashSet<String>();
+static final ImmutableSet<SomeMutableType> mutableElements = ImmutableSet.of(mutable);
+static final Logger logger = Logger.getLogger(MyClass.getName());
+static final String[] nonEmptyArray = {"these", "can", "change"};
+

These names are typically nouns or noun phrases.

+

5.2.5 Non-constant field names 

+

Non-constant field names (static or otherwise) are written +in lowerCamelCase with a preceding m_.

+

These names are typically nouns or noun phrases. For example, +m_computedValues or +m_index.

+

5.2.6 Parameter names 

+

Parameter names are written in lowerCamelCase.

One-character parameter names should be avoided.

+

5.2.7 Local variable names 

+

Local variable names are written in lowerCamelCase, and can be +abbreviated more liberally than other types of names.

However, one-character names should be avoided, except for temporary and looping variables.

Even when final and immutable, local variables are not considered to be constants, and should not +be styled as constants.

+

5.2.8 Type variable names 

+

Each type variable is named in one of two styles:

  • A single capital letter, optionally followed by a single numeral (such as + E, T, + X, T2) +
  • A name in the form used for classes (see Section 5.2.2, + Class names), followed by the capital letter + T (examples: + RequestT, + FooBarT).
+

5.3 Camel case: defined 

+

Sometimes there is more than one reasonable way to convert an English phrase into camel case, +such as when acronyms or unusual constructs like "IPv6" or "iOS" are present. To improve +predictability, Google Style specifies the following (nearly) deterministic scheme.

Beginning with the prose form of the name:

  1. Convert the phrase to plain ASCII and remove any apostrophes. For example, "Müller's + algorithm" might become "Muellers algorithm".
  2. Divide this result into words, splitting on spaces and any remaining punctuation (typically + hyphens). + +
    • Recommended: if any word already has a conventional camel-case appearance in common + usage, split this into its constituent parts (e.g., "AdWords" becomes "ad words"). Note + that a word such as "iOS" is not really in camel case per se; it defies any + convention, so this recommendation does not apply.
  3. Now lowercase everything (including acronyms), then uppercase only the first + character of: +
    • ... each word, to yield upper camel case, or
    • ... each word except the first, to yield lower camel case
  4. Finally, join all the words into a single identifier.

Note that the casing of the original words is almost entirely disregarded. Examples:

Prose formCorrectIncorrect
"XML HTTP request"XmlHttpRequestXMLHTTPRequest
"new customer ID"newCustomerIdnewCustomerID
"inner stopwatch"innerStopwatchinnerStopWatch
"supports IPv6 on iOS?"supportsIpv6OnIossupportsIPv6OnIOS
"YouTube importer"YouTubeImporter
YoutubeImporter*

*Acceptable, but not recommended.

Note: Some words are ambiguously hyphenated in the English +language: for example "nonempty" and "non-empty" are both correct, so the method names +checkNonempty and +checkNonEmpty are likewise both correct.

+

6 Programming Practices 

+ +

6.1 @Override: always used 

+

A method is marked with the @Override annotation +whenever it is legal. This includes a class method overriding a superclass method, a class method +implementing an interface method, and an interface method respecifying a superinterface +method.

Exception:@Override may be omitted when the parent method is +@Deprecated.

+

6.2 Caught exceptions: not ignored 

+

Except as noted below, it is very rarely correct to do nothing in response to a caught +exception. (Typical responses are to log it, or if it is considered "impossible", rethrow it as an +AssertionError.)

When it truly is appropriate to take no action whatsoever in a catch block, the reason this is +justified is explained in a comment.

+try {
+  int i = Integer.parseInt(response);
+  return handleNumericResponse(i);
+} catch (NumberFormatException ok) {
+  // it's not numeric; that's fine, just continue
+}
+return handleTextResponse(response);
+

Exception: In tests, a caught exception may be ignored +without comment if it is named expected. The +following is a very common idiom for ensuring that the method under test does throw an +exception of the expected type, so a comment is unnecessary here.

+try {
+  emptyStack.pop();
+  fail();
+} catch (NoSuchElementException expected) {
+}
+
+

6.3 Static members: qualified using class 

+

When a reference to a static class member must be qualified, it is qualified with that class's +name, not with a reference or expression of that class's type.

+Foo aFoo = ...;
+Foo.aStaticMethod(); // good
+aFoo.aStaticMethod(); // bad
+somethingThatYieldsAFoo().aStaticMethod(); // very bad
+
+

6.4 Finalizers: not used 

+

It is extremely rare to override Object.finalize.

Tip: Don't do it. If you absolutely must, first read and understand +Effective Java +Item 7, "Avoid Finalizers," very carefully, and then don't do it.

+

7 Javadoc 

+ +

7.1 Formatting 

+ +

7.1.1 General form 

+

The basic formatting of Javadoc blocks is as seen in this example:

+/**
+ * Multiple lines of Javadoc text are written here,
+ * wrapped normally...
+ */
+public int method(String p1) { ... }
+

... or in this single-line example:

+/** An especially short bit of Javadoc. */
+

The basic form is always acceptable. The single-line form may be substituted when there are no +at-clauses present, and the entirety of the Javadoc block (including comment markers) can fit on a +single line.

+

7.1.2 Paragraphs 

+

One blank line—that is, a line containing only the aligned leading asterisk +(*)—appears between paragraphs, and before the group of "at-clauses" if +present. Each paragraph but the first has <p> immediately before the first word, +with no space after.

+

7.1.3 At-clauses 

+

Any of the standard "at-clauses" that are used appear in the order @param, +@return, @throws, @deprecated, and these four types never +appear with an empty description. When an at-clause doesn't fit on a single line, continuation lines +are indented four (or more) spaces from the position of the @. +

+

7.2 The summary fragment 

+

The Javadoc for each class and member begins with a brief summary fragment. This +fragment is very important: it is the only part of the text that appears in certain contexts such as +class and method indexes.

This is a fragment—a noun phrase or verb phrase, not a complete sentence. It does +not begin with A {@code Foo} is a..., or +This method returns..., nor does it form a complete imperative sentence +like Save the record.. However, the fragment is capitalized and +punctuated as if it were a complete sentence.

Tip: A common mistake is to write simple Javadoc in the form +/** @return the customer ID */. This is incorrect, and should be +changed to /** Returns the customer ID. */.

+

7.3 Where Javadoc is used 

+

At the minimum, Javadoc is present for every +public class, and every +public or +protected member of such a class, with a few exceptions +noted below.

Other classes and members still have Javadoc as needed. Whenever an implementation +comment would be used to define the overall purpose or behavior of a class, method or field, that +comment is written as Javadoc instead. (It's more uniform, and more tool-friendly.)

+

7.3.1 Exception: self-explanatory methods 

+

Javadoc is optional for "simple, obvious" methods like +getFoo, in cases where there really and truly is +nothing else worthwhile to say but "Returns the foo".

Important: it is not appropriate to cite this exception to justify +omitting relevant information that a typical reader might need to know. For example, for a method +named getCanonicalName, don't omit its documentation +(with the rationale that it would say only +/** Returns the canonical name. */) if a typical reader may have no idea +what the term "canonical name" means!

+

7.3.2 Exception: overrides 

+

Javadoc is not always present on a method that overrides a supertype method. +

+
Last changed: March 21, 2014
+ + diff --git a/styleguide/javaguidelink.png b/styleguide/javaguidelink.png new file mode 100644 index 0000000000000000000000000000000000000000..75d5c7ba8dcc22b100b18b8c800da9ed99afbf7b GIT binary patch literal 189 zcmeAS@N?(olHy`uVBq!ia0vp^q9Dw{1|(OCFP#RYT0C7GLo80eoovW;K!L}#nDP3f zLaS;${>#Z0UFCva2M?aC%WS)H?QB_5g+S7$o~{tDg%>YO@zZ2dVrDwAKuzez0i`Ul zbE@l3-bt1V61%3rbUmT<%Dy%3?@ZTjdAE&Ol|^ce?3NY5cci0UGX8nXab09-b9Pp3 o=^vw)Kdk>g`TD$n)}_KZpTAr6giAPD0^P&l>FVdQ&MBb@0Ar|2 + + + + + + + + + + + + + + + + + <xsl:value-of select="@title"/> + + + + + + + +

+ + + + + + + + + + + + + + + + +
+

+ Each style point has a summary for which additional information is available + by toggling the accompanying arrow button that looks this way: + + . + You may toggle all summaries with the big arrow button: +

+
+ + + + + + + Toggle all summaries +
+
+ + + + + + + +

Parting Words

+ + + + +
+ +

+ + + + + + + + +

+ +
+ + + +
+ + + + + + + + + + + + + + + + +

+ + + + + +

+ + + + + javascript:ShowHideByName(' + + ') + + + + ?showone=# + link + + + + + + + + + + + +
+ + + + +
+ + +
+ + + + +
+ +
+ + + + + display: inline + display: none + + + +
+
+ + + +

+ + Definition: + +

+ + + +

+ + Pros: + +

+ + + +

+ + Cons: + +

+ + + +

+ + Decision: + +

+ + + +

+ +

TODO: + +
+

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +
+ + 

+           
+           
+           
+           
+             
+               
+               
+             
+           
+
+
+ + + +
+ + 

+           
+           
+           
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+             
+               
+               
+             
+           
+
+
+ + + +
+ + 

+             
+
+
+ + + +
+ + 

+                             
+
+
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+
Table of Contents
+ + + + + + + +
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