Fix foldRight implementation for iterables

libraries/stdlib/src/generated/ArraysFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun <T> Array<T>.fold(initial: T, operation: (T, T) -> T): T {
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun <T> Array<T>.foldRight(initial: T, operation: (T, T) -> T): T = reverse().fold(initial, operation)
+public inline fun <T> Array<T>.foldRight(initial: T, operation: (T, T) -> T): T = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/BooleanArraysFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun BooleanArray.fold(initial: Boolean, operation: (Boolean, Boole
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun BooleanArray.foldRight(initial: Boolean, operation: (Boolean, Boolean) -> Boolean): Boolean = reverse().fold(initial, operation)
+public inline fun BooleanArray.foldRight(initial: Boolean, operation: (Boolean, Boolean) -> Boolean): Boolean = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/ByteArraysFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun ByteArray.fold(initial: Byte, operation: (Byte, Byte) -> Byte)
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun ByteArray.foldRight(initial: Byte, operation: (Byte, Byte) -> Byte): Byte = reverse().fold(initial, operation)
+public inline fun ByteArray.foldRight(initial: Byte, operation: (Byte, Byte) -> Byte): Byte = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/CharArraysFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun CharArray.fold(initial: Char, operation: (Char, Char) -> Char)
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun CharArray.foldRight(initial: Char, operation: (Char, Char) -> Char): Char = reverse().fold(initial, operation)
+public inline fun CharArray.foldRight(initial: Char, operation: (Char, Char) -> Char): Char = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/DoubleArraysFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun DoubleArray.fold(initial: Double, operation: (Double, Double)
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun DoubleArray.foldRight(initial: Double, operation: (Double, Double) -> Double): Double = reverse().fold(initial, operation)
+public inline fun DoubleArray.foldRight(initial: Double, operation: (Double, Double) -> Double): Double = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/FloatArraysFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun FloatArray.fold(initial: Float, operation: (Float, Float) -> F
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun FloatArray.foldRight(initial: Float, operation: (Float, Float) -> Float): Float = reverse().fold(initial, operation)
+public inline fun FloatArray.foldRight(initial: Float, operation: (Float, Float) -> Float): Float = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/IntArraysFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun IntArray.fold(initial: Int, operation: (Int, Int) -> Int): Int
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun IntArray.foldRight(initial: Int, operation: (Int, Int) -> Int): Int = reverse().fold(initial, operation)
+public inline fun IntArray.foldRight(initial: Int, operation: (Int, Int) -> Int): Int = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/JUtilIteratorsFromJLangIterables.kt

@@ -143,7 +143,7 @@ public inline fun <T> java.util.Iterator<T>.fold(initial: T, operation: (T, T) -
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun <T> java.util.Iterator<T>.foldRight(initial: T, operation: (T, T) -> T): T = reverse().fold(initial, operation)
+public inline fun <T> java.util.Iterator<T>.foldRight(initial: T, operation: (T, T) -> T): T = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/LongArraysFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun LongArray.fold(initial: Long, operation: (Long, Long) -> Long)
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun LongArray.foldRight(initial: Long, operation: (Long, Long) -> Long): Long = reverse().fold(initial, operation)
+public inline fun LongArray.foldRight(initial: Long, operation: (Long, Long) -> Long): Long = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/ShortArraysFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun ShortArray.fold(initial: Short, operation: (Short, Short) -> S
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun ShortArray.foldRight(initial: Short, operation: (Short, Short) -> Short): Short = reverse().fold(initial, operation)
+public inline fun ShortArray.foldRight(initial: Short, operation: (Short, Short) -> Short): Short = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/generated/StandardFromJLangIterables.kt

@@ -145,7 +145,7 @@ public inline fun <T> Iterable<T>.fold(initial: T, operation: (T, T) -> T): T {
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun <T> Iterable<T>.foldRight(initial: T, operation: (T, T) -> T): T = reverse().fold(initial, operation)
+public inline fun <T> Iterable<T>.foldRight(initial: T, operation: (T, T) -> T): T = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/kotlin/JLangIterables.kt

@@ -135,7 +135,7 @@ public inline fun <T> java.lang.Iterable<T>.fold(initial: T, operation: (T, T) -
  *
  * @includeFunctionBody ../../test/CollectionTest.kt foldRight
  */
-public inline fun <T> java.lang.Iterable<T>.foldRight(initial: T, operation: (T, T) -> T): T = reverse().fold(initial, operation)
+public inline fun <T> java.lang.Iterable<T>.foldRight(initial: T, operation: (T, T) -> T): T = reverse().fold(initial, {x, y -> operation(y, x)})
 
 /**
  * Groups the elements in the collection into a new [[Map]] using the supplied *toKey* function to calculate the key to group the elements by

libraries/stdlib/src/kotlin/nullable/Nullables.kt

@@ -103,8 +103,8 @@ public inline fun <T> T?.fold(initial: T, operation: (it: T, it2: T) -> T): T {
  * Folds all the values from right to left with the initial value to perform the operation on sequential pairs of values
  */
 public inline fun <T> T?.foldRight(initial: T, operation: (it: T, it2: T) -> T): T {
-    // maximum size is 1 so it makes no difference :)
-    return fold(initial, operation)
+    // maximum size is 1 so reverse is not needed
+    return fold(initial, {x, y -> operation(y, x)})
 }
 
 /**

libraries/stdlib/test/CollectionTest.kt

@@ -195,13 +195,27 @@ class CollectionTest {
         }
     }
 
+    test fun foldWithNonCommutativeOperation() {
+        expect(1) {
+            val numbers = arrayList(1, 2, 3)
+            numbers.fold(7) {a, b -> a - b}
+        }
+    }
+
     test fun foldRight() {
-        expect("4321") {
+        expect("1234") {
             val numbers = arrayList(1, 2, 3, 4)
             numbers.map<Int, String>{it.toString()}.foldRight(""){ a, b -> a + b}
         }
     }
 
+    test fun foldRightWithNonCommutativeOperation() {
+        expect(-5) {
+            val numbers = arrayList(1, 2, 3)
+            numbers.foldRight(7) {a, b -> a - b}
+        }
+    }
+
     test fun groupBy() {
         val words = arrayList("a", "ab", "abc", "def", "abcd")
         val byLength = words.groupBy{ it.length }