diff --git a/libraries/stdlib/common/src/generated/_Arrays.kt b/libraries/stdlib/common/src/generated/_Arrays.kt
index 4e6674f72ae..7a9c4dad824 100644
--- a/libraries/stdlib/common/src/generated/_Arrays.kt
+++ b/libraries/stdlib/common/src/generated/_Arrays.kt
@@ -12326,7 +12326,7 @@ public inline fun CharArray.forEach(action: (Char) -> Unit): Unit {
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun <T> Array<out T>.forEachIndexed(action: (index: Int, T) -> Unit): Unit {
     var index = 0
@@ -12336,7 +12336,7 @@ public inline fun <T> Array<out T>.forEachIndexed(action: (index: Int, T) -> Uni
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun ByteArray.forEachIndexed(action: (index: Int, Byte) -> Unit): Unit {
     var index = 0
@@ -12346,7 +12346,7 @@ public inline fun ByteArray.forEachIndexed(action: (index: Int, Byte) -> Unit):
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun ShortArray.forEachIndexed(action: (index: Int, Short) -> Unit): Unit {
     var index = 0
@@ -12356,7 +12356,7 @@ public inline fun ShortArray.forEachIndexed(action: (index: Int, Short) -> Unit)
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun IntArray.forEachIndexed(action: (index: Int, Int) -> Unit): Unit {
     var index = 0
@@ -12366,7 +12366,7 @@ public inline fun IntArray.forEachIndexed(action: (index: Int, Int) -> Unit): Un
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun LongArray.forEachIndexed(action: (index: Int, Long) -> Unit): Unit {
     var index = 0
@@ -12376,7 +12376,7 @@ public inline fun LongArray.forEachIndexed(action: (index: Int, Long) -> Unit):
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun FloatArray.forEachIndexed(action: (index: Int, Float) -> Unit): Unit {
     var index = 0
@@ -12386,7 +12386,7 @@ public inline fun FloatArray.forEachIndexed(action: (index: Int, Float) -> Unit)
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun DoubleArray.forEachIndexed(action: (index: Int, Double) -> Unit): Unit {
     var index = 0
@@ -12396,7 +12396,7 @@ public inline fun DoubleArray.forEachIndexed(action: (index: Int, Double) -> Uni
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun BooleanArray.forEachIndexed(action: (index: Int, Boolean) -> Unit): Unit {
     var index = 0
@@ -12406,7 +12406,7 @@ public inline fun BooleanArray.forEachIndexed(action: (index: Int, Boolean) -> U
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun CharArray.forEachIndexed(action: (index: Int, Char) -> Unit): Unit {
     var index = 0
@@ -13591,6 +13591,114 @@ public inline fun CharArray.onEach(action: (Char) -> Unit): CharArray {
     return apply { for (element in this) action(element) }
 }
 
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@kotlin.internal.InlineOnly
+public inline fun <T> Array<out T>.onEachIndexed(action: (index: Int, T) -> Unit): Array<out T> {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@kotlin.internal.InlineOnly
+public inline fun ByteArray.onEachIndexed(action: (index: Int, Byte) -> Unit): ByteArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@kotlin.internal.InlineOnly
+public inline fun ShortArray.onEachIndexed(action: (index: Int, Short) -> Unit): ShortArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@kotlin.internal.InlineOnly
+public inline fun IntArray.onEachIndexed(action: (index: Int, Int) -> Unit): IntArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@kotlin.internal.InlineOnly
+public inline fun LongArray.onEachIndexed(action: (index: Int, Long) -> Unit): LongArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@kotlin.internal.InlineOnly
+public inline fun FloatArray.onEachIndexed(action: (index: Int, Float) -> Unit): FloatArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@kotlin.internal.InlineOnly
+public inline fun DoubleArray.onEachIndexed(action: (index: Int, Double) -> Unit): DoubleArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@kotlin.internal.InlineOnly
+public inline fun BooleanArray.onEachIndexed(action: (index: Int, Boolean) -> Unit): BooleanArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@kotlin.internal.InlineOnly
+public inline fun CharArray.onEachIndexed(action: (index: Int, Char) -> Unit): CharArray {
+    return apply { forEachIndexed(action) }
+}
+
 /**
  * Accumulates value starting with the first element and applying [operation] from left to right to current accumulator value and each element.
  * 
diff --git a/libraries/stdlib/common/src/generated/_Collections.kt b/libraries/stdlib/common/src/generated/_Collections.kt
index 9ff2f45e098..f17f249987c 100644
--- a/libraries/stdlib/common/src/generated/_Collections.kt
+++ b/libraries/stdlib/common/src/generated/_Collections.kt
@@ -1666,7 +1666,7 @@ public inline fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit {
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 public inline fun <T> Iterable<T>.forEachIndexed(action: (index: Int, T) -> Unit): Unit {
     var index = 0
@@ -1878,6 +1878,17 @@ public inline fun <T, C : Iterable<T>> C.onEach(action: (T) -> Unit): C {
     return apply { for (element in this) action(element) }
 }
 
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the collection itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+public inline fun <T, C : Iterable<T>> C.onEachIndexed(action: (index: Int, T) -> Unit): C {
+    return apply { forEachIndexed(action) }
+}
+
 /**
  * Accumulates value starting with the first element and applying [operation] from left to right to current accumulator value and each element.
  * 
diff --git a/libraries/stdlib/common/src/generated/_Maps.kt b/libraries/stdlib/common/src/generated/_Maps.kt
index dd47821fab7..7408441bff7 100644
--- a/libraries/stdlib/common/src/generated/_Maps.kt
+++ b/libraries/stdlib/common/src/generated/_Maps.kt
@@ -213,6 +213,17 @@ public inline fun <K, V, M : Map<out K, V>> M.onEach(action: (Map.Entry<K, V>) -
     return apply { for (element in this) action(element) }
 }
 
+/**
+ * Performs the given [action] on each entry, providing sequential index with the entry,
+ * and returns the map itself afterwards.
+ * @param [action] function that takes the index of an entry and the entry itself
+ * and performs the action on the entry.
+ */
+@SinceKotlin("1.4")
+public inline fun <K, V, M : Map<out K, V>> M.onEachIndexed(action: (index: Int, Map.Entry<K, V>) -> Unit): M {
+    return apply { entries.forEachIndexed(action) }
+}
+
 /**
  * Creates an [Iterable] instance that wraps the original map returning its entries when being iterated.
  */
diff --git a/libraries/stdlib/common/src/generated/_Sequences.kt b/libraries/stdlib/common/src/generated/_Sequences.kt
index 03fc73d1bde..2f48c0bf7a1 100644
--- a/libraries/stdlib/common/src/generated/_Sequences.kt
+++ b/libraries/stdlib/common/src/generated/_Sequences.kt
@@ -1115,7 +1115,7 @@ public inline fun <T> Sequence<T>.forEach(action: (T) -> Unit): Unit {
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  *
  * The operation is _terminal_.
  */
@@ -1356,6 +1356,21 @@ public fun <T> Sequence<T>.onEach(action: (T) -> Unit): Sequence<T> {
     }
 }
 
+/**
+ * Returns a sequence which performs the given [action] on each element of the original sequence as they pass through it.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ *
+ * The operation is _intermediate_ and _stateless_.
+ */
+@SinceKotlin("1.4")
+public fun <T> Sequence<T>.onEachIndexed(action: (index: Int, T) -> Unit): Sequence<T> {
+    return mapIndexed { index, element ->
+        action(index, element)
+        element
+    }
+}
+
 /**
  * Accumulates value starting with the first element and applying [operation] from left to right to current accumulator value and each element.
  *
diff --git a/libraries/stdlib/common/src/generated/_Strings.kt b/libraries/stdlib/common/src/generated/_Strings.kt
index f3db92dd03e..7f01993a1f8 100644
--- a/libraries/stdlib/common/src/generated/_Strings.kt
+++ b/libraries/stdlib/common/src/generated/_Strings.kt
@@ -1065,7 +1065,7 @@ public inline fun CharSequence.forEach(action: (Char) -> Unit): Unit {
 /**
  * Performs the given [action] on each character, providing sequential index with the character.
  * @param [action] function that takes the index of a character and the character itself
- * and performs the desired action on the character.
+ * and performs the action on the character.
  */
 public inline fun CharSequence.forEachIndexed(action: (index: Int, Char) -> Unit): Unit {
     var index = 0
@@ -1195,6 +1195,17 @@ public inline fun <S : CharSequence> S.onEach(action: (Char) -> Unit): S {
     return apply { for (element in this) action(element) }
 }
 
+/**
+ * Performs the given [action] on each character, providing sequential index with the character,
+ * and returns the char sequence itself afterwards.
+ * @param [action] function that takes the index of a character and the character itself
+ * and performs the action on the character.
+ */
+@SinceKotlin("1.4")
+public inline fun <S : CharSequence> S.onEachIndexed(action: (index: Int, Char) -> Unit): S {
+    return apply { forEachIndexed(action) }
+}
+
 /**
  * Accumulates value starting with the first character and applying [operation] from left to right to current accumulator value and each character.
  * 
diff --git a/libraries/stdlib/common/src/generated/_UArrays.kt b/libraries/stdlib/common/src/generated/_UArrays.kt
index 80670df9b91..f46db1b3ca4 100644
--- a/libraries/stdlib/common/src/generated/_UArrays.kt
+++ b/libraries/stdlib/common/src/generated/_UArrays.kt
@@ -5381,7 +5381,7 @@ public inline fun UShortArray.forEach(action: (UShort) -> Unit): Unit {
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 @SinceKotlin("1.3")
 @ExperimentalUnsignedTypes
@@ -5394,7 +5394,7 @@ public inline fun UIntArray.forEachIndexed(action: (index: Int, UInt) -> Unit):
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 @SinceKotlin("1.3")
 @ExperimentalUnsignedTypes
@@ -5407,7 +5407,7 @@ public inline fun ULongArray.forEachIndexed(action: (index: Int, ULong) -> Unit)
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 @SinceKotlin("1.3")
 @ExperimentalUnsignedTypes
@@ -5420,7 +5420,7 @@ public inline fun UByteArray.forEachIndexed(action: (index: Int, UByte) -> Unit)
 /**
  * Performs the given [action] on each element, providing sequential index with the element.
  * @param [action] function that takes the index of an element and the element itself
- * and performs the desired action on the element.
+ * and performs the action on the element.
  */
 @SinceKotlin("1.3")
 @ExperimentalUnsignedTypes
@@ -6010,6 +6010,58 @@ public inline fun UShortArray.onEach(action: (UShort) -> Unit): UShortArray {
     return apply { for (element in this) action(element) }
 }
 
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun UIntArray.onEachIndexed(action: (index: Int, UInt) -> Unit): UIntArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun ULongArray.onEachIndexed(action: (index: Int, ULong) -> Unit): ULongArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun UByteArray.onEachIndexed(action: (index: Int, UByte) -> Unit): UByteArray {
+    return apply { forEachIndexed(action) }
+}
+
+/**
+ * Performs the given [action] on each element, providing sequential index with the element,
+ * and returns the array itself afterwards.
+ * @param [action] function that takes the index of an element and the element itself
+ * and performs the action on the element.
+ */
+@SinceKotlin("1.4")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun UShortArray.onEachIndexed(action: (index: Int, UShort) -> Unit): UShortArray {
+    return apply { forEachIndexed(action) }
+}
+
 /**
  * Accumulates value starting with the first element and applying [operation] from left to right to current accumulator value and each element.
  * 
diff --git a/libraries/stdlib/test/collections/ArraysTest.kt b/libraries/stdlib/test/collections/ArraysTest.kt
index 4994437842b..51450c75faf 100644
--- a/libraries/stdlib/test/collections/ArraysTest.kt
+++ b/libraries/stdlib/test/collections/ArraysTest.kt
@@ -1441,6 +1441,23 @@ class ArraysTest {
         assertEquals(listOf('1', '2', '3'), mutableListOf<Char>().apply { charArrayOf('1', '2', '3').onEach { add(it) } })
     }
 
+    @Test fun onEachIndexed() {
+        assertEquals(listOf(1, 3, 5), mutableListOf<Int>().apply { intArrayOf(1, 2, 3).onEachIndexed { i, e -> add(i + e) } })
+        assertEquals(listOf(1, 3, 5), mutableListOf<Int>().apply { byteArrayOf(1, 2, 3).onEachIndexed { i, e -> add(i + e) } })
+        assertEquals(listOf(1, 3, 5), mutableListOf<Int>().apply { shortArrayOf(1, 2, 3).onEachIndexed { i, e -> add(i + e) } })
+        assertEquals(listOf<Long>(1, 3, 5), mutableListOf<Long>().apply { longArrayOf(1, 2, 3).onEachIndexed { i, e -> add(i + e) } })
+        assertEquals(listOf(1f, 3f, 5f), mutableListOf<Float>().apply { floatArrayOf(1f, 2f, 3f).onEachIndexed { i, e -> add(i + e) } })
+        assertEquals(listOf(1.0, 3.0, 5.0), mutableListOf<Double>().apply { doubleArrayOf(1.0, 2.0, 3.0).onEachIndexed { i, e -> add(i + e) } })
+        assertEquals(listOf(true, false, true), mutableListOf<Boolean>().apply { booleanArrayOf(true, false, false).onEachIndexed { i, e -> add(i % 2 == 0 || e) } })
+        assertEquals(listOf('1', '3', '5'), mutableListOf<Char>().apply { charArrayOf('1', '2', '3').onEachIndexed { i, e -> add(e + i) } })
+        assertEquals(listOf("a0", "b1", "c2"), mutableListOf<String>().apply { arrayOf("a", "b", "c").onEachIndexed { i, e -> add(e + i) } })
+
+        val empty = arrayOf<Int>()
+        assertSame(empty, empty.onEachIndexed { i, e -> fail("Should be unreachable: $i, $e") })
+        val nonEmpty = longArrayOf(1, 2, 3)
+        assertSame(nonEmpty, nonEmpty.onEachIndexed { _, _ -> })
+    }
+
     @Test fun drop() {
         expect(listOf(1), { intArrayOf(1).drop(0) })
         expect(listOf(), { intArrayOf().drop(1) })
diff --git a/libraries/stdlib/test/collections/IterableTests.kt b/libraries/stdlib/test/collections/IterableTests.kt
index 9be58dbaac1..ae8c16d2a66 100644
--- a/libraries/stdlib/test/collections/IterableTests.kt
+++ b/libraries/stdlib/test/collections/IterableTests.kt
@@ -313,6 +313,17 @@ abstract class IterableTests<T : Iterable<String>>(val createFrom: (Array<out St
         assertStaticTypeIs<ArrayList<Int>>(arrayListOf(1, 2, 3).onEach { })
     }
 
+    @Test
+    fun onEachIndexed() {
+        var count = 0
+        val newData = data.onEachIndexed { i, e -> count += i + e.length }
+        assertEquals(7, count)
+        assertSame(data, newData)
+
+        // static types test
+        assertStaticTypeIs<ArrayList<Int>>(arrayListOf(1, 2, 3).onEachIndexed { _, _ -> })
+    }
+
     @Test
     fun contains() {
         assertTrue(data.contains("foo"))
diff --git a/libraries/stdlib/test/collections/MapTest.kt b/libraries/stdlib/test/collections/MapTest.kt
index 45d866ac2a9..bbc62e9354d 100644
--- a/libraries/stdlib/test/collections/MapTest.kt
+++ b/libraries/stdlib/test/collections/MapTest.kt
@@ -128,6 +128,20 @@ class MapTest {
         )
     }
 
+    @Test
+    fun onEachIndexed() {
+        val map = mutableMapOf("beverage" to "beer", "location" to "Mells")
+        val result = StringBuilder()
+        val newMap = map.onEachIndexed { i, e -> result.append(i + 1).append('.').append(e.key).append("=").append(e.value).append(";") }
+        assertEquals("1.beverage=beer;2.location=Mells;", result.toString())
+        assertTrue(map === newMap)
+
+        // static types test
+        assertStaticTypeIs<HashMap<String, String>>(
+            hashMapOf("a" to "b").onEachIndexed { _, _ -> }
+        )
+    }
+
     @Test fun stream() {
         val map = mapOf("beverage" to "beer", "location" to "Mells", "name" to "James")
         val named = map.asSequence().filter { it.key == "name" }.single()
diff --git a/libraries/stdlib/test/collections/SequenceTest.kt b/libraries/stdlib/test/collections/SequenceTest.kt
index 67373311aba..824a92386d7 100644
--- a/libraries/stdlib/test/collections/SequenceTest.kt
+++ b/libraries/stdlib/test/collections/SequenceTest.kt
@@ -126,6 +126,21 @@ public class SequenceTest {
         assertEquals(sum, count)
     }
 
+    @Test
+    fun onEachIndexed() {
+        var count = 0
+        val data = sequenceOf("foo", "bar")
+        val newData = data.onEachIndexed { i, e -> count += i + e.length }
+        assertNotSame(data, newData)
+        assertEquals(0, count, "onEachIndex should be executed lazily")
+
+        data.forEach {  }
+        assertEquals(0, count, "onEachIndex should be executed only when resulting sequence is iterated")
+
+        val sum = newData.foldIndexed(0) { i, acc, e -> acc + i + e.length }
+        assertEquals(sum, count)
+    }
+
 
     @Test fun filterAndTakeWhileExtractTheElementsWithinRange() {
         assertEquals(listOf(144, 233, 377, 610, 987), fibonacci().filter { it > 100 }.takeWhile { it < 1000 }.toList())
diff --git a/libraries/stdlib/test/collections/UnsignedArraysTest.kt b/libraries/stdlib/test/collections/UnsignedArraysTest.kt
index a94f1894fb2..892f904e216 100644
--- a/libraries/stdlib/test/collections/UnsignedArraysTest.kt
+++ b/libraries/stdlib/test/collections/UnsignedArraysTest.kt
@@ -994,6 +994,21 @@ class UnsignedArraysTest {
         assertEquals(listOf<ULong>(1, 2, 3), mutableListOf<ULong>().apply { ulongArrayOf(1, 2, 3).onEach { add(it) } })
     }
 
+    @Test
+    fun onEachIndexed() {
+        assertEquals(listOf<UInt>(1, 3, 5), mutableListOf<UInt>().apply { uintArrayOf(1, 2, 3).onEachIndexed { i, e -> add(i.toUInt() + e) } })
+        assertEquals(listOf<UInt>(1, 3, 5), mutableListOf<UInt>().apply { ubyteArrayOf(1, 2, 3).onEachIndexed { i, e -> add(i.toUByte() + e) } })
+        assertEquals(listOf<UInt>(1, 3, 5), mutableListOf<UInt>().apply { ushortArrayOf(1, 2, 3).onEachIndexed { i, e -> add(i.toUShort() + e) } })
+        assertEquals(listOf<ULong>(1, 3, 5), mutableListOf<ULong>().apply { ulongArrayOf(1, 2, 3).onEachIndexed { i, e -> add(i.toULong() + e) } })
+
+        val empty = arrayOf<UInt>()
+        assertSame(empty, empty.onEachIndexed { i, e -> fail("Should be unreachable: $i, $e") })
+
+        // Identity equality for arguments of types ULongArray and ULongArray is forbidden
+//        val nonEmpty = ulongArrayOf(1, 2, 3)
+//        assertSame(nonEmpty, nonEmpty.onEachIndexed { _, _ -> })
+    }
+
     @Test
     fun drop() {
         expect(listOf(1.toUByte())) { ubyteArrayOf(1).drop(0) }
diff --git a/libraries/stdlib/test/text/StringTest.kt b/libraries/stdlib/test/text/StringTest.kt
index 957b6fb3f81..9ba2179ac71 100644
--- a/libraries/stdlib/test/text/StringTest.kt
+++ b/libraries/stdlib/test/text/StringTest.kt
@@ -948,6 +948,18 @@ class StringTest {
         assertStaticTypeIs<StringBuilder>(result.onEach { })
     }
 
+    @Test
+    fun onEachIndexed() = withOneCharSequenceArg("abcd") { data ->
+        val result = StringBuilder()
+        val newData = data.onEachIndexed { i, e -> result.append(e + i) }
+        assertEquals("aceg", result.toString())
+        assertSame(data, newData)
+
+        // static types test
+        assertStaticTypeIs<String>("x".onEachIndexed { _, _ -> })
+        assertStaticTypeIs<StringBuilder>(result.onEachIndexed { _, _ -> })
+    }
+
 
     @Test fun filter() {
         assertEquals("acdca", ("abcdcba").filter { !it.equals('b') })
diff --git a/libraries/tools/binary-compatibility-validator/reference-public-api/kotlin-stdlib-runtime-merged.txt b/libraries/tools/binary-compatibility-validator/reference-public-api/kotlin-stdlib-runtime-merged.txt
index 63d8cd63182..06ad803c221 100644
--- a/libraries/tools/binary-compatibility-validator/reference-public-api/kotlin-stdlib-runtime-merged.txt
+++ b/libraries/tools/binary-compatibility-validator/reference-public-api/kotlin-stdlib-runtime-merged.txt
@@ -2152,6 +2152,7 @@ public final class kotlin/collections/CollectionsKt {
 	public static final fun none (Ljava/lang/Iterable;)Z
 	public static final fun none (Ljava/lang/Iterable;Lkotlin/jvm/functions/Function1;)Z
 	public static final fun onEach (Ljava/lang/Iterable;Lkotlin/jvm/functions/Function1;)Ljava/lang/Iterable;
+	public static final fun onEachIndexed (Ljava/lang/Iterable;Lkotlin/jvm/functions/Function2;)Ljava/lang/Iterable;
 	public static final fun partition (Ljava/lang/Iterable;Lkotlin/jvm/functions/Function1;)Lkotlin/Pair;
 	public static final fun plus (Ljava/lang/Iterable;Ljava/lang/Iterable;)Ljava/util/List;
 	public static final fun plus (Ljava/lang/Iterable;Ljava/lang/Object;)Ljava/util/List;
@@ -2369,6 +2370,7 @@ public final class kotlin/collections/MapsKt {
 	public static final fun none (Ljava/util/Map;)Z
 	public static final fun none (Ljava/util/Map;Lkotlin/jvm/functions/Function1;)Z
 	public static final fun onEach (Ljava/util/Map;Lkotlin/jvm/functions/Function1;)Ljava/util/Map;
+	public static final fun onEachIndexed (Ljava/util/Map;Lkotlin/jvm/functions/Function2;)Ljava/util/Map;
 	public static final fun plus (Ljava/util/Map;Ljava/lang/Iterable;)Ljava/util/Map;
 	public static final fun plus (Ljava/util/Map;Ljava/util/Map;)Ljava/util/Map;
 	public static final fun plus (Ljava/util/Map;Lkotlin/Pair;)Ljava/util/Map;
@@ -4724,6 +4726,7 @@ public final class kotlin/sequences/SequencesKt {
 	public static final fun none (Lkotlin/sequences/Sequence;)Z
 	public static final fun none (Lkotlin/sequences/Sequence;Lkotlin/jvm/functions/Function1;)Z
 	public static final fun onEach (Lkotlin/sequences/Sequence;Lkotlin/jvm/functions/Function1;)Lkotlin/sequences/Sequence;
+	public static final fun onEachIndexed (Lkotlin/sequences/Sequence;Lkotlin/jvm/functions/Function2;)Lkotlin/sequences/Sequence;
 	public static final fun partition (Lkotlin/sequences/Sequence;Lkotlin/jvm/functions/Function1;)Lkotlin/Pair;
 	public static final fun plus (Lkotlin/sequences/Sequence;Ljava/lang/Iterable;)Lkotlin/sequences/Sequence;
 	public static final fun plus (Lkotlin/sequences/Sequence;Ljava/lang/Object;)Lkotlin/sequences/Sequence;
@@ -5116,6 +5119,7 @@ public final class kotlin/text/StringsKt {
 	public static final fun none (Ljava/lang/CharSequence;)Z
 	public static final fun none (Ljava/lang/CharSequence;Lkotlin/jvm/functions/Function1;)Z
 	public static final fun onEach (Ljava/lang/CharSequence;Lkotlin/jvm/functions/Function1;)Ljava/lang/CharSequence;
+	public static final fun onEachIndexed (Ljava/lang/CharSequence;Lkotlin/jvm/functions/Function2;)Ljava/lang/CharSequence;
 	public static final fun padEnd (Ljava/lang/CharSequence;IC)Ljava/lang/CharSequence;
 	public static final fun padEnd (Ljava/lang/String;IC)Ljava/lang/String;
 	public static synthetic fun padEnd$default (Ljava/lang/CharSequence;ICILjava/lang/Object;)Ljava/lang/CharSequence;
diff --git a/libraries/tools/kotlin-stdlib-gen/src/templates/Aggregates.kt b/libraries/tools/kotlin-stdlib-gen/src/templates/Aggregates.kt
index 8d00d2b7e15..b24bdbf04c6 100644
--- a/libraries/tools/kotlin-stdlib-gen/src/templates/Aggregates.kt
+++ b/libraries/tools/kotlin-stdlib-gen/src/templates/Aggregates.kt
@@ -1609,6 +1609,61 @@ object Aggregates : TemplateGroupBase() {
         }
     }
 
+    val f_onEachIndexed = fn("onEachIndexed(action: (index: Int, T) -> Unit)") {
+        includeDefault()
+        include(Maps, CharSequences, ArraysOfUnsigned)
+    } builder {
+        since("1.4")
+
+        doc {
+            """
+                Performs the given [action] on each ${f.element}, providing sequential index with the ${f.element}, 
+                and returns the ${f.collection} itself afterwards.
+                @param [action] function that takes the index of ${f.element.prefixWithArticle()} and the ${f.element} itself
+                and performs the action on the ${f.element}.
+                """
+        }
+
+        specialFor(ArraysOfObjects, ArraysOfPrimitives, ArraysOfUnsigned) {
+            inlineOnly()
+            returns("SELF")
+            body { "return apply { forEachIndexed(action) }" }
+        }
+
+        specialFor(Maps, Iterables, CharSequences) {
+            inline()
+            val collectionType = when (f) {
+                Maps -> "M"
+                CharSequences -> "S"
+                else -> "C"
+            }
+            receiver(collectionType)
+            returns(collectionType)
+            typeParam("$collectionType : SELF")
+            body { "return apply { ${if (f == Maps) "entries." else ""}forEachIndexed(action) }" }
+        }
+
+        specialFor(Sequences) {
+            returns("SELF")
+            doc {
+                """
+                Returns a sequence which performs the given [action] on each ${f.element} of the original sequence as they pass through it.
+                @param [action] function that takes the index of ${f.element.prefixWithArticle()} and the ${f.element} itself
+                and performs the action on the ${f.element}.
+                """
+            }
+            sequenceClassification(intermediate, stateless)
+            body {
+                """
+                return mapIndexed { index, element ->
+                    action(index, element)
+                    element
+                }
+                """
+            }
+        }
+    }
+
     val f_forEach = fn("forEach(action: (T) -> Unit)") {
         includeDefault()
         include(Maps, CharSequences, ArraysOfUnsigned)
@@ -1637,7 +1692,7 @@ object Aggregates : TemplateGroupBase() {
             """
             Performs the given [action] on each ${f.element}, providing sequential index with the ${f.element}.
             @param [action] function that takes the index of ${f.element.prefixWithArticle()} and the ${f.element} itself
-            and performs the desired action on the ${f.element}.
+            and performs the action on the ${f.element}.
             """ }
         returns("Unit")
         body {