Document DeferredCommand and onlyIf/onlyWhile decorators

source/docs/software/commandbased/command-compositions.rst

@@ -223,8 +223,74 @@ The ``unless()`` decorator ([Java](https://github.wpilib.org/allwpilib/docs/rele
    button.onTrue(command.unless(lambda: not intake.isDeployed()))
    ```
 
+The ``onlyIf()`` decorator ([Java](https://github.wpilib.org/allwpilib/docs/release/java/edu/wpi/first/wpilibj2/command/Command.html#onlyIf(java.util.function.BooleanSupplier)), [C++](https://github.wpilib.org/allwpilib/docs/release/cpp/classfrc2_1_1_command_ptr.html#a73b3bb7908543e6ded5901adb0667c6d), :external:py:meth:`Python <commands2.Command.onlyIf>`) is similar to ``unless()`` but with inverted logic - the command will only run if the condition is true.
+
+.. tab-set-code::
+
+   ```java
+   // Command will only run if the game piece is present
+   button.onTrue(command.onlyIf(() -> intake.hasGamePiece()));
+   ```
+
+   ```c++
+   // Command will only run if the game piece is present
+   button.OnTrue(command.OnlyIf([&intake] { return intake.HasGamePiece(); }));
+   ```
+
+   ```python
+   # Command will only run if the game piece is present
+   button.onTrue(command.onlyIf(lambda: intake.hasGamePiece()))
+   ```
+
+The ``onlyWhile()`` decorator ([Java](https://github.wpilib.org/allwpilib/docs/release/java/edu/wpi/first/wpilibj2/command/Command.html#onlyWhile(java.util.function.BooleanSupplier)), [C++](https://github.wpilib.org/allwpilib/docs/release/cpp/classfrc2_1_1_command_ptr.html#a0ef33b5e59bf0f0b42010c8d6bec4d00), :external:py:meth:`Python <commands2.Command.onlyWhile>`) composes a command with a condition that is continuously checked during execution. If the condition becomes false while the command is running, the command will be interrupted. This is backed by a ``ParallelRaceGroup`` with a ``WaitUntilCommand``.
+
+.. tab-set-code::
+
+   ```java
+   // Command will run only while the mechanism is below the target position, stopping if it reaches or exceeds the target
+   button.onTrue(command.onlyWhile(() -> mechanism.getPosition() < targetPosition));
+   ```
+
+   ```c++
+   // Command will run only while the mechanism is below the target position, stopping if it reaches or exceeds the target
+   button.OnTrue(command.OnlyWhile([&mechanism, targetPosition] { return mechanism.GetPosition() < targetPosition; }));
+   ```
+
+   ```python
+   # Command will run only while the mechanism is below the target position, stopping if it reaches or exceeds the target
+   button.onTrue(command.onlyWhile(lambda: mechanism.getPosition() < targetPosition))
+   ```
+
 ``ProxyCommand`` described below also has a constructor overload ([Java](https://github.wpilib.org/allwpilib/docs/release/java/edu/wpi/first/wpilibj2/command/ProxyCommand.html), [C++](https://github.wpilib.org/allwpilib/docs/release/cpp/classfrc2_1_1_proxy_command.html), :external:py:class:`Python <commands2.ProxyCommand>`) that calls a command-returning lambda at schedule-time and runs the returned command by proxy.
 
+The ``Defer`` factory ([Java](https://github.wpilib.org/allwpilib/docs/release/java/edu/wpi/first/wpilibj2/command/Commands.html#defer(java.util.function.Supplier,java.util.Set)), [C++](https://github.wpilib.org/allwpilib/docs/release/cpp/namespacefrc2_1_1cmd.html#a03fe6ddac82ad3a4e1c086b1c0c23422), :external:py:func:`Python <commands2.cmd.defer>`), backed by the ``DeferredCommand`` class ([Java](https://github.wpilib.org/allwpilib/docs/release/java/edu/wpi/first/wpilibj2/command/DeferredCommand.html), [C++](https://github.wpilib.org/allwpilib/docs/release/cpp/classfrc2_1_1_deferred_command.html), :external:py:class:`Python <commands2.DeferredCommand>`), defers command construction to schedule-time by calling a lambda that returns a command. Unlike ``ProxyCommand``, the deferred command runs inline within the composition, keeping everything within the composition instead of delegating to the scheduler. This should generally be preferred over the deferred ``ProxyCommand`` constructor.
+
+.. tab-set-code::
+
+   ```java
+   // Selects one of two commands based on current sensor state when scheduled
+   Commands.defer(
+      () -> sensor.get() ? Commands.print("Sensor true") : Commands.print("Sensor false"),
+      Set.of()
+   )
+   ```
+
+   ```c++
+   // Selects one of two commands based on current sensor state when scheduled
+   frc2::cmd::Defer(
+      [&sensor] { return sensor.Get() ? frc2::cmd::Print("Sensor true") : frc2::cmd::Print("Sensor false"); },
+      {}
+   )
+   ```
+
+   ```python
+   # Selects one of two commands based on current sensor state when scheduled
+   commands2.cmd.defer(
+      lambda: commands2.cmd.print_("Sensor true") if sensor.get() else commands2.cmd.print_("Sensor false"),
+      []
+   )
+   ```
+
 ### Scheduling Other Commands
 
 By default, composition members are run through the command composition, and are never themselves seen by the scheduler. Accordingly, their requirements are added to the composition's requirements. While this is usually fine, sometimes it is undesirable for the entire command composition to gain the requirements of a single command. A good solution is to "fork off" from the command composition and schedule that command separately. However, this requires synchronization between the composition and the individually-scheduled command.