Make mappedBy lazy.

runtime/lib/byte_array.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.
 
 patch class Int8List {
   /* patch */ factory Int8List(int length) {
     return new _Int8Array(length);
   }
 
   /* patch */ factory Int8List.view(ByteArray array,
@@ skipping 114 matching lines @@
 
   bool contains(element) => Collections.contains(this, element);
 
   void forEach(void f(element)) {
     var len = this.length;
     for (var i = 0; i < len; i++) {
       f(this[i]);
     }
   }
 
-  Collection mappedBy(f(element)) {
-    return Collections.mappedBy(this, new List(), f);
+  Iterable mappedBy(f(element)) {
+    return new MappedIterable<int, dynamic>(this, f);
   }
 
   Dynamic reduce(Dynamic initialValue,
                  Dynamic combine(Dynamic initialValue, element)) {
     return Collections.reduce(this, initialValue, combine);
   }
 
   Collection where(bool f(element)) {
     return Collections.where(this, new List(), f);
   }
@@ skipping 1458 matching lines @@
   int setFloat64(int byteOffset, double value) {
     return _array._setFloat64(_offset + byteOffset, value);
   }
 
   final _ByteArrayBase _array;
   final int _offset;
   final int _length;
 }
 
 
-class _ByteArrayViewBase {
+class _ByteArrayViewBase extends Collection<int> {

[Ivan Posva, 2012/11/26 18:29:09]

Please see previous comment about extra costs of extending vs implementing.

[floitsch, 2012/11/28 13:48:23]

It is much easier if we only have to implement our functions in one place. When
things stabilize we can remove the extend and copy the functions back.
Added a TODO to make sure we don't forget.

   abstract num operator[](int index);
 
   // Methods implementing the Collection interface.
 
   void forEach(void f(element)) {
     var len = this.length;
     for (var i = 0; i < len; i++) {
       f(this[i]);
     }
   }
 
-  Collection mappedBy(f(element)) {
-    return Collections.mappedBy(this, new List(), f);
-  }
-
-  Dynamic reduce(Dynamic initialValue,
-                 Dynamic combine(Dynamic initialValue, element)) {
-    return Collections.reduce(this, initialValue, combine);
-  }
-
-  Collection where(bool f(element)) {
-    return Collections.where(this, new List(), f);
-  }
-
-  bool every(bool f(element)) {
-    return Collections.every(this, f);
-  }
-
-  bool some(bool f(element)) {
-    return Collections.some(this, f);;
-  }
-
   bool get isEmpty {
     return this.length == 0;
   }
 
   abstract int get length;
 
   // Methods implementing the List interface.
 
   set length(newLength) {
     throw new UnsupportedError(
@@ skipping 765 matching lines @@
     }
     _rangeCheck(this.length, start, length);
     return _array.subByteArray(_offset + start, length);
   }
 
   static const int _BYTES_PER_ELEMENT = 8;
   final ByteArray _array;
   final int _offset;
   final int _length;
 }