Writing Modules & Commands

This guide will teach you how to create advanced modules, use submodules, and write custom commands, including command factories.

Modules & Submodules

Modules can contain other modules, creating a hierarchy. This is useful for grouping related systems. For example, a Robot module can contain Intake, Outtake, and Drivetrain modules.

Kotlin

object Robot : Module(Intake, Outtake, Drivetrain) {
    // Robot module manages Intake, Outtake, and Drivetrain
    // When you register Robot, all submodules are automatically registered!
}

Java

public class Robot extends Module {
    public static final Robot INSTANCE = new Robot();

    public Robot() {
        super(Intake.INSTANCE, Outtake.INSTANCE, Drivetrain.INSTANCE);
    }
}

Writing Commands

Commands are reusable actions. You can define them as standalone classes or use helper functions.

Basic Commands

You can write simple commands directly inside your modules.

Kotlin

object Intake : Module() {
    // ... (motor setup)

    val absorb = instant { motor.power = 1.0 }
    val eject = instant { motor.power = -1.0 }
    val stop = instant { motor.power = 0.0 }
}

Java

public class Intake extends Module {
    // ... (motor setup)

    public final InstantCommand absorb = new InstantCommand(() -> motor.setPower(1.0));
    public final InstantCommand eject = new InstantCommand(() -> motor.setPower(-1.0));
    public final InstantCommand stop = new InstantCommand(() -> motor.setPower(0.0));
}

Command Factories

Sometimes you need commands that take parameters, like “Go to position X”. Instead of creating a new command class for every possible position, you can use a Command Factory.

A command factory is simply a method that returns a new Command instance configured with the given parameters.

Kotlin

object Lift : Module() {
    // ... (motor setup)

    fun goToPosition(targetPosition: Int): Command {
        return instant {
            motor.targetPosition = targetPosition
            motor.mode = DcMotor.RunMode.RUN_TO_POSITION
            motor.power = 1.0
        }
    }
}

Java

public class Lift extends Module {
    // ... (motor setup)

    public Command goToPosition(int targetPosition) {
        return new InstantCommand(() -> {
            motor.setTargetPosition(targetPosition);
            motor.setMode(DcMotor.RunMode.RUN_TO_POSITION);
            motor.setPower(1.0);
        });
    }
}

Warning: Loop Flooding

Be careful when using command factories inside a loop! Every time you call goToPosition(100), it creates a new command instance. If you call this every loop cycle (e.g., inside onMainLoop), you will flood the command scheduler with hundreds of identical commands per second, causing severe lag or crashes.

Do NOT do this:

// BAD! Creates a new command every loop!
public void onMainLoop() {
    if (gamepad1.a) {
        Lift.INSTANCE.goToPosition(100).register();
    }
}

Instead, use a trigger or check if it’s already running:

// GOOD! Only registers once when the button is pressed.
if (gamepad1.wasJustPressed(GamepadKeys.Button.A)) {
    Lift.INSTANCE.goToPosition(100).register();
}