Scan functions for Sequences and Iterable #KT-7657

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

@@ -1288,6 +1288,104 @@ public inline fun CharSequence.reduceRightOrNull(operation: (Char, acc: Char) ->
     return accumulator
 }
 
+/**
+ * Returns a list containing successive accumulation values generated by applying [operation] from left to right
+ * to each character and current accumulator value that starts with [initial] value.
+ * 
+ * Note that `acc` value passed to [operation] function should not be mutated;
+ * otherwise it would affect the previous value in resulting list.
+ * 
+ * @param [operation] function that takes current accumulator value and a character, and calculates the next accumulator value.
+ * 
+ * @sample samples.collections.Collections.Aggregates.scan
+ */
+@SinceKotlin("1.3")
+@ExperimentalStdlibApi
+public inline fun <R> CharSequence.scan(initial: R, operation: (acc: R, Char) -> R): List<R> {
+    if (isEmpty()) return listOf(initial)
+    val result = ArrayList<R>(length + 1).apply { add(initial) }
+    var accumulator = initial
+    for (element in this) {
+        accumulator = operation(accumulator, element)
+        result.add(accumulator)
+    }
+    return result
+}
+
+/**
+ * Returns a list containing successive accumulation values generated by applying [operation] from left to right
+ * to each character, its index in the original char sequence and current accumulator value that starts with [initial] value.
+ * 
+ * Note that `acc` value passed to [operation] function should not be mutated;
+ * otherwise it would affect the previous value in resulting list.
+ * 
+ * @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.scan
+ */
+@SinceKotlin("1.3")
+@ExperimentalStdlibApi
+public inline fun <R> CharSequence.scanIndexed(initial: R, operation: (index: Int, acc: R, Char) -> R): List<R> {
+    if (isEmpty()) return listOf(initial)
+    val result = ArrayList<R>(length + 1).apply { add(initial) }
+    var accumulator = initial
+    for (index in indices) {
+        accumulator = operation(index, accumulator, this[index])
+        result.add(accumulator)
+    }
+    return result
+}
+
+/**
+ * Returns a list containing successive accumulation values generated by applying [operation] from left to right
+ * to each character and current accumulator value that starts with the first character of this char sequence.
+ * 
+ * Note that `acc` value passed to [operation] function should not be mutated;
+ * otherwise it would affect the previous value in resulting list.
+ * 
+ * @param [operation] function that takes current accumulator value and a character, and calculates the next accumulator value.
+ * 
+ * @sample samples.collections.Collections.Aggregates.scanReduce
+ */
+@SinceKotlin("1.3")
+@ExperimentalStdlibApi
+public inline fun CharSequence.scanReduce(operation: (acc: Char, Char) -> Char): List<Char> {
+    if (isEmpty()) return emptyList()
+    var accumulator = this[0]
+    val result = ArrayList<Char>(length).apply { add(accumulator) }
+    for (index in 1 until length) {
+        accumulator = operation(accumulator, this[index])
+        result.add(accumulator)
+    }
+    return result
+}
+
+/**
+ * Returns a list containing successive accumulation values generated by applying [operation] from left to right
+ * to each character, its index in the original char sequence and current accumulator value that starts with the first character of this char sequence.
+ * 
+ * Note that `acc` value passed to [operation] function should not be mutated;
+ * otherwise it would affect the previous value in resulting list.
+ * 
+ * @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.scanReduce
+ */
+@SinceKotlin("1.3")
+@ExperimentalStdlibApi
+public inline fun CharSequence.scanReduceIndexed(operation: (index: Int, acc: Char, Char) -> Char): List<Char> {
+    if (isEmpty()) return emptyList()
+    var accumulator = this[0]
+    val result = ArrayList<Char>(length).apply { add(accumulator) }
+    for (index in 1 until length) {
+        accumulator = operation(index, accumulator, this[index])
+        result.add(accumulator)
+    }
+    return result
+}
+
 /**
  * Returns the sum of all values produced by [selector] function applied to each character in the char sequence.
  */