Recommit changing List.skip/take/revert returns Iterable and remove mappedBy.

tests/corelib/iterable_skip_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 main() {
   List<int> list1 = <int>[1, 2, 3];
   List<int> list2 = const <int>[4, 5];
   List<String> list3 = <String>[];
   Set<int> set1 = new Set<int>();
   set1..add(11)
       ..add(12)
       ..add(13);
   Set set2 = new Set();
 
   Iterable<int> skip0 = list1.skip(0);
-  Expect.isTrue(skip0 is List);
+  Expect.isTrue(skip0 is! List);
   Iterator<int> it = skip0.iterator;
   Expect.isNull(it.current);
   Expect.isTrue(it.moveNext());
   Expect.equals(1, it.current);
   Expect.isTrue(it.moveNext());
   Expect.equals(2, it.current);
   Expect.isTrue(it.moveNext());
   Expect.equals(3, it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   Iterable<int> skip1 = list1.skip(1);
-  Expect.isTrue(skip1 is List);
-  Expect.isTrue(skip1.skip(2).skip(1) is List);
+  Expect.isTrue(skip1 is! List);
+  Expect.isTrue(skip1.skip(2).skip(1) is! List);
   it = skip1.iterator;
   Expect.isNull(it.current);
   Expect.isTrue(it.moveNext());
   Expect.equals(2, it.current);
   Expect.isTrue(it.moveNext());
   Expect.equals(3, it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   Iterable<int> skip2 = list1.skip(2);
-  Expect.isTrue(skip2 is List);
-  Expect.isTrue(skip2.skip(2).skip(1) is List);
+  Expect.isTrue(skip2 is! List);
+  Expect.isTrue(skip2.skip(2).skip(1) is! List);
   it = skip2.iterator;
   Expect.isNull(it.current);
   Expect.isTrue(it.moveNext());
   Expect.equals(3, it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   Iterable<int> skip3 = list1.skip(3);
-  Expect.isTrue(skip3 is List);
-  Expect.isTrue(skip3.skip(2).skip(1) is List);
+  Expect.isTrue(skip3 is! List);
+  Expect.isTrue(skip3.skip(2).skip(1) is! List);
   it = skip3.iterator;
   Expect.isNull(it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   Iterable<int> skip4 = list1.skip(4);
-  Expect.isTrue(skip4 is List);
-  Expect.isTrue(skip4.skip(2).skip(1) is List);
+  Expect.isTrue(skip4 is! List);
+  Expect.isTrue(skip4.skip(2).skip(1) is! List);
   it = skip4.iterator;
   Expect.isNull(it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   skip0 = list1.skip(0);
   skip1 = skip0.skip(1);
   skip2 = skip1.skip(1);
   skip3 = skip2.skip(1);
   skip4 = skip3.skip(1);
@@ skipping 24 matching lines @@
   it = skip3.iterator;
   Expect.isNull(it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
   it = skip4.iterator;
   Expect.isNull(it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   skip0 = list2.skip(0);
-  Expect.isTrue(skip0 is List);
-  Expect.isTrue(skip0.skip(2).skip(1) is List);
+  Expect.isTrue(skip0 is! List);
+  Expect.isTrue(skip0.skip(2).skip(1) is! List);
   it = skip0.iterator;
   Expect.isNull(it.current);
   Expect.isTrue(it.moveNext());
   Expect.equals(4, it.current);
   Expect.isTrue(it.moveNext());
   Expect.equals(5, it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   skip1 = list2.skip(1);
-  Expect.isTrue(skip1 is List);
-  Expect.isTrue(skip1.skip(2).skip(1) is List);
+  Expect.isTrue(skip1 is! List);
+  Expect.isTrue(skip1.skip(2).skip(1) is! List);
   it = skip1.iterator;
   Expect.isNull(it.current);
   Expect.isTrue(it.moveNext());
   Expect.equals(5, it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   skip2 = list2.skip(2);
-  Expect.isTrue(skip2 is List);
-  Expect.isTrue(skip2.skip(2).skip(1) is List);
+  Expect.isTrue(skip2 is! List);
+  Expect.isTrue(skip2.skip(2).skip(1) is! List);
   it = skip2.iterator;
   Expect.isNull(it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   skip3 = list2.skip(3);
-  Expect.isTrue(skip3 is List);
-  Expect.isTrue(skip3.skip(2).skip(1) is List);
+  Expect.isTrue(skip3 is! List);
+  Expect.isTrue(skip3.skip(2).skip(1) is! List);
   it = skip3.iterator;
   Expect.isNull(it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   Iterable<String> skip02 = list3.skip(0);
-  Expect.isTrue(skip02 is List);
-  Expect.isTrue(skip02.skip(2).skip(1) is List);
+  Expect.isTrue(skip02 is! List);
+  Expect.isTrue(skip02.skip(2).skip(1) is! List);
   Iterator<String> it2 = skip02.iterator;
   Expect.isNull(it2.current);
   Expect.isFalse(it2.moveNext());
   Expect.isNull(it2.current);
 
   Iterable<String> skip12 = list3.skip(1);
-  Expect.isTrue(skip12 is List);
-  Expect.isTrue(skip12.skip(2).skip(1) is List);
+  Expect.isTrue(skip12 is! List);
+  Expect.isTrue(skip12.skip(2).skip(1) is! List);
   it2 = skip12.iterator;
   Expect.isNull(it2.current);
   Expect.isFalse(it2.moveNext());
   Expect.isNull(it2.current);
 
   skip0 = set1.skip(0);
   List<int> copied = skip0.toList();
   Expect.equals(3, copied.length);
   Expect.isTrue(set1.contains(copied[0]));
   Expect.isTrue(set1.contains(copied[1]));
@@ skipping 54 matching lines @@
   it = skip0.iterator;
   Expect.isNull(it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
   skip1 = set2.skip(1);
   it = skip1.iterator;
   Expect.isNull(it.current);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
+
+  testSkipTake(Iterable input, int skip, int take) {
+    List expected = [];
+    Iterator iter = input.iterator;
+    for (int i = 0; i < skip; i++) iter.moveNext();
+    for (int i = 0; i < take; i++) {
+      if (!iter.moveNext()) break;
+      expected.add(iter.current);
+    }
+    Expect.listEquals(expected, input.skip(skip).take(take).toList());
+  }
+
+  List longList = [1, 4, 5, 3, 8, 11, 12, 6, 9, 10, 13, 7, 2, 14, 15];
+  Set bigSet = longList.toSet();
+
+  for (Iterable collection in [longList, longList.reversed, bigSet]) {
+    testSkipTake(collection, 0, 0);
+    testSkipTake(collection, 0, 5);
+    testSkipTake(collection, 0, 15);
+    testSkipTake(collection, 0, 25);
+    testSkipTake(collection, 5, 0);
+    testSkipTake(collection, 5, 5);
+    testSkipTake(collection, 5, 10);
+    testSkipTake(collection, 5, 20);
+    testSkipTake(collection, 15, 0);
+    testSkipTake(collection, 15, 5);
+    testSkipTake(collection, 20, 0);
+    testSkipTake(collection, 20, 5);
+  }
 }