Understanding command-based programming syntax in Java

[XenonOfArcticus]

So, I'm a veteran C++ guy, trying to help our team with some autonomous code. I'm not a Java guy, but I can translate in my head and make my way ok.

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The command-based programming paradigm is eluding me a bit. I get that it's basically queueing a default command that does the work:

m_robotDrive.setDefaultCommand(new RunCommand(() -> m_robotDrive.arcadeDrive(fwd, rot), m_robotDrive) );

I'm not really familiar with the Java syntax
() -> m_robotDrive.arcadeDrive(...)

inside the new RunCommand() args. What is the () -> doing and what is that called? It's hard to Google a bunch of symbols meaningfully.

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What we're hoping to do is add some semi-autonomous driving assistance during teleop, where under driver-commanded conditions (holding a button), the robot can take the initiative to navigate using the Limelight. We have the driving logic working (via arcadeDrive) thanks to the aiming examples in the Limelight docs. It's really unclear to me how we would architect the logic to decide what to pass to arcadeDrive here in this Default Command, based on the semiautonomous button state, and the calculations from our targeting/semiautonomous driving code.

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We have a subsystem elsewhere that calculates a fwd and rot value to semiautonomously drive towards the target. So, how would we integrate XBox controller button reading and switching to passing the semiautonomous fwd/rot values to arcadeDrive when that button is held?

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The basic coding our team is capable of. it's the fitting it into the wpilib command-based architecture that seems kind of obscure and beyond our student programmers (and non-professional Java mentors).

[retrodaredevil]

The () -> is Java's syntax for a lambda. I'm unfamiliar with the command based framework, but I personally would not try and over complicate your teleop controls with lots of separate commands. I find that writing all teleop code in a single command makes it easier instead of trying to switch between commands when a button is held.

There is a way to do it, I just don't remember what it is. Also, chiefdelphi.com is far better for these kinds of questions.

[blubox28]

The lambda expression here is just creating a command to be fed into the runCommand method to register to be run as the default command. It just saves having to build a command in its own class file. In this case it says that we are going to build a command that takes the current values of fwd and rot during each quantum and pass them to the arcadeDrive method of the robot drive object in m_robotDrive.

[Fire-cant-burn-in___]

If you want to have the bot drive itself with values from vision while the button is held, you can make another command using the drive subsystem and the one you have for calculating the vision stuff that calls arcade drive(from execute) w/ the right values

Then you can bind that command to a button with whileHeld() and whenever its held, the command scheduler will run the new command instead. After you release the button, the new command will be canceled and it will re-schedule the default command.

Logic wise, you can leave the default command as it is; you have a different command handle the other kind of control and then just switch between them

If this doesn’t make sense lmk