Provide dropLastWhile for Arrays, Lists and Strings.

libraries/stdlib/src/generated/_Filtering.kt

@@ -189,6 +189,133 @@ public fun String.drop(n: Int): String {
     return substring(Math.min(n, length()))
 }
 
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun <T> Array<out T>.dropLastWhile(predicate: (T) -> Boolean): List<T> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun BooleanArray.dropLastWhile(predicate: (Boolean) -> Boolean): List<Boolean> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun ByteArray.dropLastWhile(predicate: (Byte) -> Boolean): List<Byte> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun CharArray.dropLastWhile(predicate: (Char) -> Boolean): List<Char> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun DoubleArray.dropLastWhile(predicate: (Double) -> Boolean): List<Double> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun FloatArray.dropLastWhile(predicate: (Float) -> Boolean): List<Float> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun IntArray.dropLastWhile(predicate: (Int) -> Boolean): List<Int> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun LongArray.dropLastWhile(predicate: (Long) -> Boolean): List<Long> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun ShortArray.dropLastWhile(predicate: (Short) -> Boolean): List<Short> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a list containing all elements except last elements that satisfy the given [predicate].
+ */
+public inline fun <T> List<T>.dropLastWhile(predicate: (T) -> Boolean): List<T> {
+    for (index in lastIndex downTo 0) {
+        if (!predicate(this[index])) {
+            return take(index + 1)
+        }
+    }
+    return emptyList()
+}
+
+/**
+ * Returns a string containing all characters except last characters that satisfy the given [predicate].
+ */
+public inline fun String.dropLastWhile(predicate: (Char) -> Boolean): String {
+    return trimEnd(predicate)
+}
+
 /**
  * Returns a list containing all elements except first elements that satisfy the given [predicate].
  */
@@ -369,11 +496,7 @@ public fun <T> Stream<T>.dropWhile(predicate: (T) -> Boolean): Stream<T> {
  * Returns a string containing all characters except first characters that satisfy the given [predicate].
  */
 public inline fun String.dropWhile(predicate: (Char) -> Boolean): String {
-    for (index in 0..length - 1)
+    return trimStart(predicate)
-        if (!predicate(get(index))) {
-            return substring(index)
-        }
-    return ""
 }
 
 /**

libraries/stdlib/test/collections/CollectionTest.kt

@@ -273,6 +273,14 @@ class CollectionTest {
         assertEquals(listOf("bar", "abc"), coll.dropWhile { it.startsWith("f") })
     }
 
+    test fun dropLastWhile() {
+        val coll = listOf("Foo", "bare", "abc" )
+        assertEquals(coll, coll.dropLastWhile { false })
+        assertEquals(listOf<String>(), coll.dropLastWhile { true })
+        assertEquals(listOf("Foo", "bare"), coll.dropLastWhile { it.length() < 4 })
+        assertEquals(listOf("Foo"), coll.dropLastWhile { it.all { it in 'a'..'z' } })
+    }
+
     test fun take() {
         val coll = listOf("foo", "bar", "abc")
         assertEquals(listOf("foo"), coll.take(1))

libraries/tools/kotlin-stdlib-gen/src/templates/Filtering.kt

@@ -170,11 +170,7 @@ fun filtering(): List<GenericFunction> {
         returns(Strings) { "String" }
         body(Strings) {
             """
-            for (index in 0..length - 1)
+            return trimStart(predicate)
-                if (!predicate(get(index))) {
-                    return substring(index)
-                }
-            return ""
             """
         }
 
@@ -228,6 +224,32 @@ fun filtering(): List<GenericFunction> {
         }
     }
 
+    templates add f("dropLastWhile(predicate: (T) -> Boolean)") {
+        inline(true)
+        only(Lists, ArraysOfObjects, ArraysOfPrimitives, Strings)
+        doc { "Returns a list containing all elements except last elements that satisfy the given [predicate]." }
+        returns("List<T>")
+
+        body {
+            """
+            for (index in lastIndex downTo 0) {
+                if (!predicate(this[index])) {
+                    return take(index + 1)
+                }
+            }
+            return emptyList()
+            """
+        }
+
+        doc(Strings) { "Returns a string containing all characters except last characters that satisfy the given [predicate]." }
+        returns("String", Strings)
+        body(Strings) {
+            """
+            return trimEnd(predicate)
+            """
+        }
+    }
+
     templates add f("filter(predicate: (T) -> Boolean)") {
         inline(true)