Command based programming
The command-based paradigm is also an example of declarative programming - A style of software which focuses on describing what a program should do, rather than how it gets done
A user can specify that “the robot should perform an action when a condition is true” (note the use of a lambda):
new Trigger(condition::get).onTrue(Commands.runOnce(() -> piston.set(DoubleSolenoid.Value.kForward)));
In contrast, without using command-based, the user would need to check the button state every iteration, and perform the appropriate action based on the state of the button.
![[command-cloud.png]]
The command-based pattern is based around two core abstractions: commands, and subsystems. - only one command can use a given subsystem at the same time. - subsystems allow users to “hide” the internal complexity of their actual hardware from the rest of their code
Commands are run by the CommandScheduler singleton, which polls triggers (such as buttons) for commands to schedule, preventing resource conflicts, and executing scheduled commands
The scheduler’s run() method must be called; it is generally recommended to call it from the robotPeriodic() method of the Robot class, which is run at a default frequency of 50Hz (once every 20ms)
Multiple commands can run concurrently, as long as they do not require the same resources on the robot. - commands specify which subsystems they interact with - scheduler will ensure that no more more than one command requiring a given subsystem is scheduled at a time