Class Cached

src/main/java/field/utility/Cached.java:15–82

Handy Utility class for guarding computation of function with a check-function This is a Function and you can give a function 'witness' that's . If the witness function returns something that's different from the last time it returned (or this cache has been

 * return value stored and return. Otherwise, you get the same result as before.
 */
public class Cached<t_check, t_witness, t_value> implements Function<t_check, t_value> {

	private BiFunction<t_check, t_value, t_value> compute;
	private final Function<t_check, t_witness> witness;
	private t_witness valid;
	private t_value value;
	private boolean invalid = false;
	private String debug = null;

	public Cached(BiFunction<t_check, t_value, t_value> compute, Function<t_check, t_witness> witness) {
		this.witness = witness;
		this.compute = compute;
		invalid = true;
	}

	public Cached<t_check, t_witness, t_value> setCompute(BiFunction<t_check, t_value, t_value> compute) {
		this.compute = compute;
		return this;
	}

	public Cached<t_check, t_witness, t_value> invalidate() {
		if (debug != null) Log.log("cached." + debug, ()->" cache invalidated :");
		invalid = true;
		return this;
	}

	public t_value apply(t_check check) {
		t_witness w;
		try {
			w = witness.apply(check);
		}
		catch(Throwable t)
		{
			System.err.println(" exception thrown by witness :"+witness+" carying on");
			t.printStackTrace();
			w=null;
			invalid = true;
		}

		t_witness finalW = w;
		if (invalid || !Util.safeEq(w, valid)) {
			if (debug != null) {
				Log.log("cached." + debug, ()->" cache invalid :" + invalid + " " + finalW + " " + valid + " " + Util.safeEq(finalW, valid));
			}
			value = compute.apply(check, value);
			valid = w;

			if (valid instanceof Mutable)
				valid = (t_witness) ((Mutable)valid).duplicate();

			invalid = false;
		} else if (debug != null)
			Log.log("cached." + debug,()-> " cache valid :" + invalid + " " + finalW + " " + valid + " " + Util.safeEq(finalW, valid));
		return value;
	}

	public Cached<t_check, t_witness, t_value> debugOn(String name) {
		this.debug = name;