Add takeLast method for String, lists and arrays.

Check the parameter n in drop, take and takeLast methods.

libraries/stdlib/src/generated/_Filtering.kt

@@ -13,12 +13,12 @@ import java.util.Collections // TODO: it's temporary while we have java.util.Col
  * Returns a list containing all elements except first [n] elements
  */
 public fun <T> Array<out T>.drop(n: Int): List<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
-    var count = 0
     val list = ArrayList<T>(size() - n)
-    for (item in this) {
-        if (count++ >= n) list.add(item)
+    for (index in n..size() - 1) {
+        list.add(this[index])
     }
     return list
 }
@@ -27,12 +27,12 @@ public fun <T> Array<out T>.drop(n: Int): List<T> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun BooleanArray.drop(n: Int): List<Boolean> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
-    var count = 0
     val list = ArrayList<Boolean>(size() - n)
-    for (item in this) {
-        if (count++ >= n) list.add(item)
+    for (index in n..size() - 1) {
+        list.add(this[index])
     }
     return list
 }
@@ -41,12 +41,12 @@ public fun BooleanArray.drop(n: Int): List<Boolean> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun ByteArray.drop(n: Int): List<Byte> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
-    var count = 0
     val list = ArrayList<Byte>(size() - n)
-    for (item in this) {
-        if (count++ >= n) list.add(item)
+    for (index in n..size() - 1) {
+        list.add(this[index])
     }
     return list
 }
@@ -55,12 +55,12 @@ public fun ByteArray.drop(n: Int): List<Byte> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun CharArray.drop(n: Int): List<Char> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
-    var count = 0
     val list = ArrayList<Char>(size() - n)
-    for (item in this) {
-        if (count++ >= n) list.add(item)
+    for (index in n..size() - 1) {
+        list.add(this[index])
     }
     return list
 }
@@ -69,12 +69,12 @@ public fun CharArray.drop(n: Int): List<Char> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun DoubleArray.drop(n: Int): List<Double> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
-    var count = 0
     val list = ArrayList<Double>(size() - n)
-    for (item in this) {
-        if (count++ >= n) list.add(item)
+    for (index in n..size() - 1) {
+        list.add(this[index])
     }
     return list
 }
@@ -83,12 +83,12 @@ public fun DoubleArray.drop(n: Int): List<Double> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun FloatArray.drop(n: Int): List<Float> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
-    var count = 0
     val list = ArrayList<Float>(size() - n)
-    for (item in this) {
-        if (count++ >= n) list.add(item)
+    for (index in n..size() - 1) {
+        list.add(this[index])
     }
     return list
 }
@@ -97,12 +97,12 @@ public fun FloatArray.drop(n: Int): List<Float> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun IntArray.drop(n: Int): List<Int> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
-    var count = 0
     val list = ArrayList<Int>(size() - n)
-    for (item in this) {
-        if (count++ >= n) list.add(item)
+    for (index in n..size() - 1) {
+        list.add(this[index])
     }
     return list
 }
@@ -111,12 +111,12 @@ public fun IntArray.drop(n: Int): List<Int> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun LongArray.drop(n: Int): List<Long> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
-    var count = 0
     val list = ArrayList<Long>(size() - n)
-    for (item in this) {
-        if (count++ >= n) list.add(item)
+    for (index in n..size() - 1) {
+        list.add(this[index])
     }
     return list
 }
@@ -125,12 +125,12 @@ public fun LongArray.drop(n: Int): List<Long> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun ShortArray.drop(n: Int): List<Short> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
-    var count = 0
     val list = ArrayList<Short>(size() - n)
-    for (item in this) {
-        if (count++ >= n) list.add(item)
+    for (index in n..size() - 1) {
+        list.add(this[index])
     }
     return list
 }
@@ -139,6 +139,7 @@ public fun ShortArray.drop(n: Int): List<Short> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun <T> Collection<T>.drop(n: Int): List<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     if (n >= size())
         return emptyList()
     var count = 0
@@ -153,6 +154,7 @@ public fun <T> Collection<T>.drop(n: Int): List<T> {
  * Returns a list containing all elements except first [n] elements
  */
 public fun <T> Iterable<T>.drop(n: Int): List<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     var count = 0
     val list = ArrayList<T>()
     for (item in this) {
@@ -161,10 +163,25 @@ public fun <T> Iterable<T>.drop(n: Int): List<T> {
     return list
 }
 
+/**
+ * Returns a list containing all elements except first [n] elements
+ */
+public fun <T> List<T>.drop(n: Int): List<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    if (n >= size())
+        return emptyList()
+    val list = ArrayList<T>(size() - n)
+    for (index in n..size() - 1) {
+        list.add(this[index])
+    }
+    return list
+}
+
 /**
  * Returns a sequence containing all elements except first [n] elements
  */
 public fun <T> Sequence<T>.drop(n: Int): Sequence<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     return DropSequence(this, n)
 }
 
@@ -174,6 +191,7 @@ deprecated("Migrate to using Sequence<T> and respective functions")
  * Returns a stream containing all elements except first [n] elements
  */
 public fun <T> Stream<T>.drop(n: Int): Stream<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     return DropStream(this, n)
 }
 
@@ -961,6 +979,7 @@ public fun String.slice(indices: Iterable<Int>): String {
  * Returns a list containing first [n] elements
  */
 public fun <T> Array<out T>.take(n: Int): List<T> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<T>(realN)
@@ -976,6 +995,7 @@ public fun <T> Array<out T>.take(n: Int): List<T> {
  * Returns a list containing first [n] elements
  */
 public fun BooleanArray.take(n: Int): List<Boolean> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<Boolean>(realN)
@@ -991,6 +1011,7 @@ public fun BooleanArray.take(n: Int): List<Boolean> {
  * Returns a list containing first [n] elements
  */
 public fun ByteArray.take(n: Int): List<Byte> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<Byte>(realN)
@@ -1006,6 +1027,7 @@ public fun ByteArray.take(n: Int): List<Byte> {
  * Returns a list containing first [n] elements
  */
 public fun CharArray.take(n: Int): List<Char> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<Char>(realN)
@@ -1021,6 +1043,7 @@ public fun CharArray.take(n: Int): List<Char> {
  * Returns a list containing first [n] elements
  */
 public fun DoubleArray.take(n: Int): List<Double> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<Double>(realN)
@@ -1036,6 +1059,7 @@ public fun DoubleArray.take(n: Int): List<Double> {
  * Returns a list containing first [n] elements
  */
 public fun FloatArray.take(n: Int): List<Float> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<Float>(realN)
@@ -1051,6 +1075,7 @@ public fun FloatArray.take(n: Int): List<Float> {
  * Returns a list containing first [n] elements
  */
 public fun IntArray.take(n: Int): List<Int> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<Int>(realN)
@@ -1066,6 +1091,7 @@ public fun IntArray.take(n: Int): List<Int> {
  * Returns a list containing first [n] elements
  */
 public fun LongArray.take(n: Int): List<Long> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<Long>(realN)
@@ -1081,6 +1107,7 @@ public fun LongArray.take(n: Int): List<Long> {
  * Returns a list containing first [n] elements
  */
 public fun ShortArray.take(n: Int): List<Short> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<Short>(realN)
@@ -1096,6 +1123,7 @@ public fun ShortArray.take(n: Int): List<Short> {
  * Returns a list containing first [n] elements
  */
 public fun <T> Collection<T>.take(n: Int): List<T> {
+    require(n >= 0, "Requested element count $n is less than zero.")
     var count = 0
     val realN = if (n > size()) size() else n
     val list = ArrayList<T>(realN)
@@ -1111,6 +1139,7 @@ public fun <T> Collection<T>.take(n: Int): List<T> {
  * Returns a list containing first [n] elements
  */
 public fun <T> Iterable<T>.take(n: Int): List<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     var count = 0
     val list = ArrayList<T>(n)
     for (item in this) {
@@ -1125,6 +1154,7 @@ public fun <T> Iterable<T>.take(n: Int): List<T> {
  * Returns a sequence containing first *n* elements
  */
 public fun <T> Sequence<T>.take(n: Int): Sequence<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     return TakeSequence(this, n)
 }
 
@@ -1134,6 +1164,7 @@ deprecated("Migrate to using Sequence<T> and respective functions")
  * Returns a stream containing first *n* elements
  */
 public fun <T> Stream<T>.take(n: Int): Stream<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
     return TakeStream(this, n)
 }
 
@@ -1144,6 +1175,143 @@ public fun String.take(n: Int): String {
     return substring(0, Math.min(n, length()))
 }
 
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun <T> Array<out T>.takeLast(n: Int): List<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<T>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun BooleanArray.takeLast(n: Int): List<Boolean> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<Boolean>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun ByteArray.takeLast(n: Int): List<Byte> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<Byte>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun CharArray.takeLast(n: Int): List<Char> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<Char>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun DoubleArray.takeLast(n: Int): List<Double> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<Double>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun FloatArray.takeLast(n: Int): List<Float> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<Float>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun IntArray.takeLast(n: Int): List<Int> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<Int>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun LongArray.takeLast(n: Int): List<Long> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<Long>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun ShortArray.takeLast(n: Int): List<Short> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<Short>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a list containing last [n] elements
+ */
+public fun <T> List<T>.takeLast(n: Int): List<T> {
+    require(n >= 0, { "Requested element count $n is less than zero." })
+    val size = size()
+    val realN = if (n > size) size else n
+    val list = ArrayList<T>(realN)
+    for (index in size - realN .. size - 1)
+        list.add(this[index])
+    return list
+}
+
+/**
+ * Returns a string containing the last [n] characters from this string, or the entire string if this string is shorter
+ */
+public fun String.takeLast(n: Int): String {
+    return substring(length() - Math.min(n, length()), length())
+}
+
 /**
  * Returns a list containing first elements satisfying the given [predicate]
  */

libraries/stdlib/test/collections/ArraysJVMTest.kt

@@ -216,6 +216,7 @@ class ArraysJVMTest {
     }
 
     test fun drop() {
+        expect(listOf(1), { intArray(1).drop(0) })
         expect(listOf(), { intArray().drop(1) })
         expect(listOf(), { intArray(1).drop(1) })
         expect(listOf(3), { intArray(2, 3).drop(1) })
@@ -227,6 +228,9 @@ class ArraysJVMTest {
         expect(listOf(false), { booleanArray(true, false).drop(1) })
         expect(listOf('b'), { charArray('a', 'b').drop(1) })
         expect(listOf("b"), { array("a", "b").drop(1) })
+        fails {
+            listOf(2).drop(-1)
+        }
     }
 
     test fun dropWhile() {
@@ -245,6 +249,7 @@ class ArraysJVMTest {
 
     test fun take() {
         expect(listOf(), { intArray().take(1) })
+        expect(listOf(), { intArray(1).take(0) })
         expect(listOf(1), { intArray(1).take(1) })
         expect(listOf(2), { intArray(2, 3).take(1) })
         expect(listOf(3000000000000), { longArray(3000000000000, 2000000000000).take(1) })
@@ -255,6 +260,27 @@ class ArraysJVMTest {
         expect(listOf(true), { booleanArray(true, false).take(1) })
         expect(listOf('a'), { charArray('a', 'b').take(1) })
         expect(listOf("a"), { array("a", "b").take(1) })
+        fails {
+            listOf(1).take(-1)
+        }
+    }
+
+    test fun takeLast() {
+        expect(listOf(), { intArray().takeLast(1) })
+        expect(listOf(), { intArray(1).takeLast(0) })
+        expect(listOf(1), { intArray(1).takeLast(1) })
+        expect(listOf(3), { intArray(2, 3).takeLast(1) })
+        expect(listOf(2000000000000), { longArray(3000000000000, 2000000000000).takeLast(1) })
+        expect(listOf(3.toByte()), { byteArray(2, 3).takeLast(1) })
+        expect(listOf(3.toShort()), { shortArray(2, 3).takeLast(1) })
+        expect(listOf(3.0f), { floatArray(2f, 3f).takeLast(1) })
+        expect(listOf(3.0), { doubleArray(2.0, 3.0).takeLast(1) })
+        expect(listOf(false), { booleanArray(true, false).takeLast(1) })
+        expect(listOf('b'), { charArray('a', 'b').takeLast(1) })
+        expect(listOf("b"), { array("a", "b").takeLast(1) })
+        fails {
+            listOf(1).takeLast(-1)
+        }
     }
 
     test fun takeWhile() {

libraries/stdlib/test/text/StringJVMTest.kt

@@ -332,5 +332,12 @@ class StringJVMTest {
         assertEquals("BCDabc", builder.slice(1..6))
         assertEquals("baD", builder.slice(5 downTo 3))
         assertEquals("aDAB", builder.slice(iter))
+
+        fails {
+            "abc".slice(listOf(1,4))
+        }
+        fails {
+            builder.slice(listOf(10))
+        }
     }
 }