From 852e21fe7ef96f2cc581200b0d8d94340151fb71 Mon Sep 17 00:00:00 2001
From: James Strachan <james.strachan@gmail.com>
Date: Sat, 7 Jan 2012 07:49:54 +0000
Subject: [PATCH] added Iterable<T>.reverse() along with foldRight(init, op)

---
 stdlib/ktSrc/JavaIterables.kt  | 19 ++++++++++++++++++-
 testlib/test/CollectionTest.kt | 24 ++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/stdlib/ktSrc/JavaIterables.kt b/stdlib/ktSrc/JavaIterables.kt
index d299d6485a6..8815f7e929d 100644
--- a/stdlib/ktSrc/JavaIterables.kt
+++ b/stdlib/ktSrc/JavaIterables.kt
@@ -82,7 +82,7 @@ inline fun <T> java.lang.Iterable<T>.foreach(operation: (element: T) -> Unit) {
 }
 
 /**
- * Folds all the values from from left to right using the initial value to perform the operation on sequential pairs of values
+ * Folds all the values from from left to right with the initial value to perform the operation on sequential pairs of values
  *
  * For example to sum together all numeric values in a collection of numbers it would be
  * {code}val total = numbers.fold(0){(a, b) -> a + b}{code}
@@ -95,6 +95,14 @@ inline fun <T> java.lang.Iterable<T>.fold(initial: T, operation: (it: T, it2: T)
   return answer
 }
 
+/**
+ * Folds all the values from right to left with the initial value to perform the operation on sequential pairs of values
+ */
+inline fun <T> java.lang.Iterable<T>.foldRight(initial: T, operation: (it: T, it2: T) -> T): T {
+  val reversed = this.reverse()
+  return reversed.fold(initial, operation)
+}
+
 /**
  * Iterates through the collection performing the transformation on each element and using the result
  * as the key in a map to group elements by the result
@@ -124,6 +132,15 @@ inline fun <T> java.lang.Iterable<T>.join(separator: String, prefix: String = ""
   return buffer.toString().sure()
 }
 
+/** Returns a reversed List of this collection */
+inline fun <T> java.lang.Iterable<T>.reverse() : List<T> {
+  val answer = LinkedList<T>()
+  for (elem in this) {
+    answer.addFirst(elem)
+  }
+  return answer
+}
+
 inline fun <T, C: Collection<T>> java.lang.Iterable<T>.to(result: C) : C {
   for (elem in this)
     result.add(elem)
diff --git a/testlib/test/CollectionTest.kt b/testlib/test/CollectionTest.kt
index bf570281b2c..c479553458e 100644
--- a/testlib/test/CollectionTest.kt
+++ b/testlib/test/CollectionTest.kt
@@ -140,8 +140,27 @@ class CollectionTest() : TestSupport() {
       val numbers = arrayList<Int>()
       numbers.fold(0){(it, it2) -> it + it2}
     }
+
+    expect("1234") {
+      val numbers = arrayList(1, 2, 3, 4)
+
+      // TODO would be nice to be able to write this as this
+      // numbers.map{it.toString()}.fold(""){it + it2}
+      numbers.map<Int,String>{it.toString()}.fold(""){(it, it2) -> it + it2}
+    }
   }
 
+  fun testFoldRight() {
+    expect("4321") {
+      val numbers = arrayList(1, 2, 3, 4)
+
+      // TODO would be nice to be able to write this as this
+      // numbers.map{it.toString()}.foldRight(""){it + it2}
+      numbers.map<Int,String>{it.toString()}.foldRight(""){(it, it2) -> it + it2}
+    }
+  }
+
+
   fun testGroupBy() {
     val words = arrayList("a", "ab", "abc", "def", "abcd")
     /*
@@ -179,6 +198,11 @@ class CollectionTest() : TestSupport() {
     assertEquals(arrayList(3, 3), lengths)
   }
 
+  fun testReverse() {
+    val rev = data.reverse()
+    assertEquals(arrayList("bar", "foo"), rev)
+  }
+
   fun testSort() {
     val coll: List<String> = arrayList("foo", "bar", "abc")