Java generics are too limited to do what we need. This refactors generic code previously in Unit and Measure into unit-specific classes that can have unit-safe math operations (notably, times and divide) that can return values in known units instead of a wildcarded Measure<?>.
Unit-specific measure implementations are automatically generated by ./wpiunits/generate_units.py, which generates generic interfaces and mutable and immutable implementations of those interfaces. These make up the bulk of the diff of this PR (approximately 9300 LOC).
This also adds units for angular and linear velocities, accelerations, and momenta; moment of inertia; and torque.
Group memory doxygen into one module.
Remove concept alias and add doxygen definitions for foonathan memory.
\concept was added as a doxygen command in 1.9.2 and is meant to be applied to concepts. Inserting them into standard comment paragraphs causes doxygen to interpret the following text as a concept name and add it to the documentation, as well as remove the text from the paragraph.
In the upstream repo, this alias links to markdown documentation, so it's not usable for us anyways.
That, plus adding the doxygen definitions/aliases from upstream cleans up most of the errors/weird output from doxygen for foonathan memory.
This adds support for two serialization formats for complex data types:
- Protobuf for complex objects with variable length internals that need forward and backward wire compatibility (lower speed, more flexible)
- Raw struct (ByteBuffer-style) for fixed-length objects (higher speed, less flexible)
Deserialization can be done either by creating a new object (for immutable objects) or overwriting the contents of an existing object (for mutable objects).
Implementing classes should provide inner classes that implement the Protobuf or Struct interface (in Java) or specialize the wpi::Protobuf or wpi::Struct struct (in C++). It is possible for classes to implement both. If the class itself does not implement serialization, it's possible for third parties/users to provide an implementation instead.
Uses the Google protobuf implementation for C++ and the QuickBuffers alternative protobuf implementation for Java.
# Background
Unit safety has always been a problem in WPILib. Any value corresponding to a physical measurement, such as current draw or distance traveled, is represented by a bare number with no unit tied to it; it's up to the programmer to know what units they're working and take care to remember that while working on their robot program. This leads to bugs when programmers accidentally mix units without knowing, or measure something (such as a wheel diameter) in one unit and program using another. `wpiunits` is intended to eliminate that class of bugs.
Another source of friction is the controllers and models in `wpimath` that expect all inputs to be in terms of SI units (meter, kilogram, and so on), while most FRC teams are US-based and most commonly use imperial units. wpimath does a good job of noting unit types in method names and argument names; however, it still relies on users properly converting values (and knowing they even have to do so).
# API
There are really only two core classes in this library: `Unit` and `Measure`. A `Unit` represents some dimension like distance or time. `Unit` is subclassed to define specific dimensions (eg `Distance` and `Time`) and those subclasses are instantiated to defined particular units in those dimensions, such as `Meters` and `Feet` being instances of the `Distance` class.
A `Measure` is a value tied to a particular dimension like distance and knows what unit that value is tied to. `Measure` has two implementations - one immutable and one mutable. The `Measure` interface only defines *read-only* operations; any API working with measurements should use the interface. The default implementation is `ImmutableMeasure`, which only implements those read-only operations and is useful for tracking constants. `MutableMeasure` also adds some methods that will allow for mutation of its internal state; this class is intended for use for things like sensors and controllers that track internal state and don't want to allocate new `Measure` objects every time something like `myEncoder.getDistance()` is called. However, the APIs for those methods should still only expose the read-only `Measure` interface so users can't (without casting or reflection) change the internal values.
A `Units` class provides convenient definitions for most of the commonly used unit types, such as `Meters`, `Feet`, and `Milliseconds`. I recommend static importing these units eg `import static edu.wpi.first.units.Units.Meters`) so they can be used like `Meters.of(1.234)` instead of `Units.Meters.of(1.234)`
# Examples
These examples are admittedly contrived. Users shouldn't be interacting much with measure objects themselves, since wpimath and wpilibj classes will be updated to support working with them; users will often just have to take a `Measure` output from one place (such as an encoder) and feed it as input to something else (such as a PID controller or kinematics model)
```java
// Using raw units
Encoder encoder = ...
int kPulsesPerRev = 2048;
double kWheelDiameterMeters = Units.inchesToMeters(6);
double kGearRatio = 10.86;
// always have to remember this encoder will output in meters!
encoder.setDistancePerPulse(kWheelDiameterMeters * Math.PI / (kGearRatio * kPulsesPerRev));
Command driveDistance(double distance) {
// have to know the distance argument needs to be in meters!
return run(this::driveStraight).until(() -> encoder.getDistance() >= distance);
}
// Oops! This will go 16 feet, not 5!
Command driveFiveFeet = driveDistance(5);
Command driveOneMeter = driveDistance(1);
```
```java
// Using wpiunits
Encoder encoder = ...
int kPulsesPerRev = 2048;
Measure<Distance> kWheelDiameter = Inches.of(6);
double kGearRatio = 10.86;
encoder.setDistancePerPulse(kWheelDiameter.times(Math.PI).divide(kGearRatio * kPulsesPerRev));
Command driveDistance(Measure<Distance> distance) {
// Measure#gte automatically handles unit conversions
return run(this::driveStraight).until(() -> encoder.getDistance().gte(distance));
}
// Users HAVE to be explicit about their units
Command driveFiveFeet = driveDistance(Feet.of(5));
Command driveOneMeter = driveDistance(Meters.of(1));
```
```java
SmartDashboard.putNumber("Temperature (C)", pdp.getTemperature().in(Celsius));
SmartDashboard.putNumber("Temperature (F)", pdp.getTemperature().in(Fahrenheit));
```
```java
var InchSecond = Inch.mult(Second); // new combined unit types can be user-defined
var InchPerSecond = Inch.per(Second);
PIDController<Distance, ElectricPotential> heightController = new PIDController<>(
/* kP */ Volts.of(0.2).per(Inch),
/* kI */ Volts.of(0.002).per(InchSecond),
/* kD */ Volts.of(0.008).per(InchPerSecond)
);
var elevatorTop = Feet.of(4).plus(Inches.of(6.125));
elevatorMotor.setVoltage(heightController.calculate(encoder.getDistance(), elevatorTop));
```
* Use explicit this capture required by C++20
* Use C++20 span
* Replace wpi::numbers with std::numbers
* Fix C++20 clang-tidy warning false positive in fmt
* Remove ciso646 include since C++20 removed that header
* Fix global-buffer-overflow asan warnings in ntcore tests
* Add DIOSetProxy constructor to HAL
* Upgrade MSVC compiler to 2022
* Bump native-utils to 2023.2.7 (changes to std=c++20)
Co-authored-by: Peter Johnson <johnson.peter@gmail.com>
