Implement reduceIndexedOrNull and reduceRightIndexedOrNull #KT-36866

libraries/stdlib/common/src/generated/_Strings.kt

@@ -1220,6 +1220,26 @@ public inline fun CharSequence.reduceIndexed(operation: (index: Int, acc: Char,
     return accumulator
 }
 
+/**
+ * Accumulates value starting with the first character and applying [operation] from left to right
+ * to current accumulator value and each character with its index in the original char sequence.
+ * Returns null if the char sequence is empty.
+ * @param [operation] function that takes the index of a character, current accumulator value
+ * and the character itself and calculates the next accumulator value.
+ * 
+ * @sample samples.collections.Collections.Aggregates.reduceOrNull
+ */
+@SinceKotlin("1.4")
+public inline fun CharSequence.reduceIndexedOrNull(operation: (index: Int, acc: Char, Char) -> Char): Char? {
+    if (isEmpty())
+        return null
+    var accumulator = this[0]
+    for (index in 1..lastIndex) {
+        accumulator = operation(index, accumulator, this[index])
+    }
+    return accumulator
+}
+
 /**
  * Accumulates value starting with the first character and applying [operation] from left to right to current accumulator value and each character. Returns null if the char sequence is empty.
  * 
@@ -1271,6 +1291,27 @@ public inline fun CharSequence.reduceRightIndexed(operation: (index: Int, Char,
     return accumulator
 }
 
+/**
+ * Accumulates value starting with last character and applying [operation] from right to left
+ * to each character with its index in the original char sequence and current accumulator value.
+ * Returns null if the char sequence is empty.
+ * @param [operation] function that takes the index of a character, the character itself
+ * and current accumulator value, and calculates the next accumulator value.
+ * 
+ * @sample samples.collections.Collections.Aggregates.reduceRightOrNull
+ */
+@SinceKotlin("1.4")
+public inline fun CharSequence.reduceRightIndexedOrNull(operation: (index: Int, Char, acc: Char) -> Char): Char? {
+    var index = lastIndex
+    if (index < 0) return null
+    var accumulator = get(index--)
+    while (index >= 0) {
+        accumulator = operation(index, get(index), accumulator)
+        --index
+    }
+    return accumulator
+}
+
 /**
  * Accumulates value starting with last character and applying [operation] from right to left to each character and current accumulator value. Returns null if the char sequence is empty.
  *