Implemented lazy variant of IHolder

1 files changed, 90 insertions, 0 deletions

diff --git a/BJC-Utils2/src/main/java/bjc/utils/data/LazyHolder.java b/BJC-Utils2/src/main/java/bjc/utils/data/LazyHolder.java
new file mode 100644
index 0000000..db5b6ef
--- /dev/null
+++ b/BJC-Utils2/src/main/java/bjc/utils/data/LazyHolder.java
@@ -0,0 +1,90 @@
+package bjc.utils.data;
+
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+import bjc.utils.funcdata.FunctionalList;
+
+/**
+ * Holds a single value of a specific type. This is used for indirect
+ * references to data, and more specifically for accessing non-final
+ * variables from a lambda. AKA the identity monad
+ * 
+ * This is a lazy variant of {@link IHolder}
+ * 
+ * @author ben
+ *
+ * @param <T>
+ *            The type of the data being held
+ */
+public class LazyHolder<T> implements IHolder<T> {
+	/**
+	 * The source for a value held by this lazy holder
+	 */
+	private Supplier<T>						heldSrc;
+
+	/**
+	 * The value internally held by this lazy holder
+	 */
+	private T								held;
+
+	/**
+	 * List of queued actions to be performed on realized values
+	 */
+	private FunctionalList<Function<T, T>>	actions;
+
+	/**
+	 * Create a new lazy holder with the given supplier
+	 * 
+	 * @param src
+	 *            The supplier for a value when it is neededs
+	 */
+	public LazyHolder(Supplier<T> src) {
+		heldSrc = src;
+
+		held = null;
+	}
+
+	/**
+	 * Create a new lazy holder with the given value
+	 * 
+	 * @param val
+	 *            The value held in the holder
+	 */
+	public LazyHolder(T val) {
+		held = val;
+	}
+
+	@Override
+	public <NewT> IHolder<NewT> map(Function<T, NewT> f) {
+		return new LazyHolder<NewT>(() -> {
+			if (held == null) {
+				return actions.reduceAux(heldSrc.get(),
+						Function<T, T>::apply, f::apply);
+			} else {
+				return actions.reduceAux(held, Function<T, T>::apply,
+						f::apply);
+			}
+		});
+	}
+
+	@Override
+	public IHolder<T> transform(Function<T, T> f) {
+		actions.add(f);
+
+		return this;
+	}
+
+	@Override
+	public <E> E unwrap(Function<T, E> f) {
+		// Actualize ourselves
+		if (held == null) {
+			held = heldSrc.get();
+		}
+
+		actions.forEach((act) -> held = act.apply(held));
+
+		return f.apply(held);
+	}
+
+}