Added a conditional command that chooses 1 of 2 commands (#435)

Tests and documentation for ConditionalCommand were also added. This is a fixed version of #9, so it doesn't support lambdas.

Closes #9

wpilibc/shared/include/Commands/ConditionalCommand.h

@@ -0,0 +1,81 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2017. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <string>
+
+#include "Commands/Command.h"
+#include "Commands/InstantCommand.h"
+
+namespace frc {
+
+/**
+ * A {@link ConditionalCommand} is a {@link Command} that starts one of two
+ * commands.
+ *
+ * <p>
+ * A {@link ConditionalCommand} uses m_condition to determine whether it should
+ * run m_onTrue or m_onFalse.
+ * </p>
+ *
+ * <p>
+ * A {@link ConditionalCommand} adds the proper {@link Command} to the {@link
+ * Scheduler} during {@link ConditionalCommand#initialize()} and then {@link
+ * ConditionalCommand#isFinished()} will return true once that {@link Command}
+ * has finished executing.
+ * </p>
+ *
+ * <p>
+ * If no {@link Command} is specified for m_onFalse, the occurrence of that
+ * condition will be a no-op.
+ * </p>
+ *
+ * @see Command
+ * @see Scheduler
+ */
+class ConditionalCommand : public Command {
+ public:
+  explicit ConditionalCommand(Command* onTrue,
+                              Command* onFalse = new InstantCommand());
+  ConditionalCommand(const std::string& name, Command* onTrue,
+                     Command* onFalse = new InstantCommand());
+  virtual ~ConditionalCommand() = default;
+
+ protected:
+  /**
+   * The Condition to test to determine which Command to run.
+   *
+   * @return true if m_onTrue should be run or false if m_onFalse should be run.
+   */
+  virtual bool Condition() = 0;
+
+  void _Initialize() override;
+  void _Cancel() override;
+  bool IsFinished() override;
+  void Interrupted() override;
+
+ private:
+  /**
+   * The Command to execute if {@link ConditionalCommand#Condition()} returns
+   * true
+   */
+  Command* m_onTrue;
+
+  /**
+   * The Command to execute if {@link ConditionalCommand#Condition()} returns
+   * false
+   */
+  Command* m_onFalse;
+
+  /**
+   * Stores command chosen by condition
+   */
+  Command* m_chosenCommand = nullptr;
+};
+
+}  // namespace frc