1 files changed, 112 insertions, 0 deletions
diff --git a/src/main/java/bjc/data/Identity.java b/src/main/java/bjc/data/Identity.java
new file mode 100644
index 0000000..8645c4c
--- /dev/null
+++ b/src/main/java/bjc/data/Identity.java
@@ -0,0 +1,112 @@
+package bjc.data;
+
+import java.util.function.Function;
+import java.util.function.UnaryOperator;
+
+/**
+ * Simple implementation of IHolder that has no hidden behavior.
+ *
+ * @author ben
+ *
+ * @param <ContainedType>
+ *        The type contained in the holder.
+ */
+public class Identity<ContainedType> implements IHolder<ContainedType> {
+	/* The held value. */
+	private ContainedType heldValue;
+
+	/** Create a holder holding null */
+	public Identity() {
+		heldValue = null;
+	}
+
+	/**
+	 * Create a holder holding the specified value.
+	 *
+	 * @param value
+	 *        The value to hold.
+	 */
+	public Identity(final ContainedType value) {
+		heldValue = value;
+	}
+
+	@Override
+	public <BoundType> IHolder<BoundType> bind(final Function<ContainedType, IHolder<BoundType>> binder) {
+		return binder.apply(heldValue);
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+
+		result = prime * result + (heldValue == null ? 0 : heldValue.hashCode());
+
+		return result;
+	}
+
+	@Override
+	public boolean equals(final Object obj) {
+		if(this == obj) return true;
+		if(obj == null) return false;
+		if(!(obj instanceof Identity)) return false;
+
+		final Identity<?> other = (Identity<?>) obj;
+
+		if(heldValue == null) {
+			if(other.heldValue != null) return false;
+		} else if(!heldValue.equals(other.heldValue)) return false;
+
+		return true;
+	}
+
+	@Override
+	public <NewType> Function<ContainedType, IHolder<NewType>> lift(final Function<ContainedType, NewType> func) {
+		return (val) -> {
+			return new Identity<>(func.apply(val));
+		};
+	}
+
+	@Override
+	public <MappedType> IHolder<MappedType> map(final Function<ContainedType, MappedType> mapper) {
+		return new Identity<>(mapper.apply(heldValue));
+	}
+
+	@Override
+	public String toString() {
+		return String.format("Identity [heldValue=%s]", heldValue);
+	}
+
+	@Override
+	public IHolder<ContainedType> transform(final UnaryOperator<ContainedType> transformer) {
+		heldValue = transformer.apply(heldValue);
+
+		return this;
+	}
+
+	@Override
+	public <UnwrappedType> UnwrappedType unwrap(final Function<ContainedType, UnwrappedType> unwrapper) {
+		return unwrapper.apply(heldValue);
+	}
+
+	/**
+	 * Create a new identity container.
+	 *
+	 * @param val
+	 *        The contained value.
+	 *
+	 * @return A new identity container.
+	 */
+	public static <ContainedType> Identity<ContainedType> id(final ContainedType val) {
+		return new Identity<>(val);
+	}
+
+	/**
+	 * Create a new empty identity container.
+	 *
+	 * @return A new empty identity container.
+	 */
+	public static <ContainedType> Identity<ContainedType> id() {
+		return new Identity<>();
+	}
+}