Add $.memoize(function) method.

Author: javadev

src/main/java/com/github/underscore/$.java

@@ -1294,10 +1294,19 @@ public List<List<T>> chunk(final int size) {
         return chunk(getIterable(), size);
     }
 
-    public static <T, F> Function1<T, F> bind(final Function1<T, F> function) {
-        return new Function1<T, F>() {
+    public static <T, F> Function1<F, T> bind(final Function1<F, T> function) {
+        return new Function1<F, T>() {
             @Override
-            public F apply(T arg) {
+            public T apply(F arg) {
+                return function.apply(arg);
+            }
+        };
+    }
+
+    public static <T, F> Function1<F, T> memoize(final Function1<F, T> function) {
+        return new MemoizeFunction1<F, T>() {
+            @Override
+            public T calc(F arg) {
                 return function.apply(arg);
             }
         };

src/main/java/com/github/underscore/MemoizeFunction1.java

@@ -1,13 +1,13 @@
 package com.github.underscore;
 
-import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.Map;
 
-public abstract class MemoizeFunction1<T> implements Function1<T, T> {
-    private final Map<T, T> cache = new HashMap<T, T>();
-    public abstract T calc(final T n);
+public abstract class MemoizeFunction1<F, T> implements Function1<F, T> {
+    private final Map<F, T> cache = new LinkedHashMap<F, T>();
+    public abstract T calc(final F n);
 
-    public T apply(final T key) {
+    public T apply(final F key) {
         if (!cache.containsKey(key)) {
             cache.put(key, calc(key));
         }

src/test/java/com/github/underscore/FunctionsTest.java

@@ -84,12 +84,19 @@ public Integer apply(final Integer arg2) {
 */
     @Test
     public void memoize() {
-        class FibonacciFuncion1 extends MemoizeFunction1<Integer> {
+        class FibonacciFuncion1 extends MemoizeFunction1<Integer, Integer> {
             public Integer calc(final Integer n) {
                 return n < 2 ? n : apply(n - 1) + apply(n - 2);
             }
         }
         assertEquals(55, new FibonacciFuncion1().apply(10).intValue());
+        Function1<Integer, Integer> memoizeFunction = $.memoize(
+            new Function1<Integer, Integer>() {
+                public Integer apply(final Integer n) {
+                    return n < 2 ? n : apply(n - 1) + apply(n - 2);
+                }
+            });
+        assertEquals(55, memoizeFunction.apply(10).intValue());
     }
 
 /*