Class Cache

src/main/java/fieldbox/ui/Compositor.java:128–155

	}

	static public class Cache<T> {
		private final Function<T, Long> getMod;
		private final Consumer<T> update;
		T target;
		long mod;
		boolean lock = false;

		public Cache(T target, Function<T, Long> getMod, Consumer<T> update) {
			this.target = target;
			this.mod = getMod.apply(target) - 1;
			this.getMod = getMod;
			this.update = update;
		}

		public void update() {
			if (lock) return;
			try {
				lock = true;
				long m = getMod.apply(target);
				if (m != mod) {
					update.accept(target);
					mod = getMod.apply(target);
				}
			} finally {
				lock = false;
			}
		}
	}

	public class Layer {
		public Map<Layer, Cache<Layer>> dependsOn = new HashMap<>();