Resolve #22. More general reduce interface

aNNiMON · Jan 22, 2016 · 820ef8b · 820ef8b
1 parent 48bdf90
commit 820ef8b
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diff --git a/src/main/java/com/annimon/stream/Stream.java b/src/main/java/com/annimon/stream/Stream.java
@@ -641,13 +641,31 @@ public void forEach(final Consumer<? super T> action) {
      * @param accumulator  the accumulation function
      * @return the result of the reduction
      */
-    public T reduce(final T identity, BiFunction<T, T, T> accumulator) {
+    /*public T reduce(final T identity, BiFunction<T, T, T> accumulator) {
         T result = identity;
         while (iterator.hasNext()) {
             final T value = iterator.next();
             result = accumulator.apply(result, value);
         }
         return result;
+    }*/
+
+    /**
+     * Reduces the elements using provided identity value and the associative accumulation function.
+     * 
+     * <p>This is a terminal operation.
+     * 
+     * @param identity  the initial value
+     * @param accumulator  the accumulation function
+     * @return the result of the reduction
+     */
+    public <R> R reduce(R identity, BiFunction<? super R, ? super T, ? extends R> accumulator) {
+        R result = identity;
+        while (iterator.hasNext()) {
+            final T value = iterator.next();
+            result = accumulator.apply(result, value);
+        }
+        return result;
     }
 
     /**

diff --git a/src/test/java/com/annimon/stream/StreamTest.java b/src/test/java/com/annimon/stream/StreamTest.java
@@ -502,6 +502,18 @@ public void testReduceSumFromMinus45() {
         assertEquals(0, result);
     }
 
+    @Test
+    public void testReduceWithAnotherType() {
+        int result = Stream.of("a", "bb", "ccc", "dddd")
+                .reduce(0, new BiFunction<Integer, String, Integer>() {
+                    @Override
+                    public Integer apply(Integer length, String s) {
+                        return length + s.length();
+                    }
+                });
+        assertEquals(10, result);
+    }
+
     @Test
     public void testReduceOptional() {
         Optional<Integer> result = Stream.ofRange(0, 10)
@@ -538,6 +550,25 @@ public void testCollectWithSupplierAndAccumulator() {
         assertEquals("abcdefg", text);
     }
 
+    @Test
+    public void testCollect123() {
+        String string123 = Stream.of("1", "2", "3")
+                .collect(new Supplier<StringBuilder>() {
+                    @Override
+                    public StringBuilder get() {
+                        return new StringBuilder();
+                    }
+                }, new BiConsumer<StringBuilder, String>() {
+
+                    @Override
+                    public void accept(StringBuilder value1, String value2) {
+                        value1.append(value2);
+                    }
+                })
+                .toString();
+        assertEquals("123", string123);
+    }
+
     @Test
     public void testMin() {
         Optional<Integer> min = Stream.of(6, 3, 9, 0, -7, 19)