runCondition property

Optional condition that determines whether this system should run.

If null, the system always runs. If non-null, the condition is evaluated before each run and the system is skipped if it returns false.

final system = FunctionSystem(
  'playerInput',
  runIf: (world) => world.getResource<GameState>()?.isPlaying ?? false,
  run: (world) { /* ... */ },
);