Add EfficientLength marker interface to some iterabels.

sdk/lib/collection/list.dart

 // Copyright (c) 2013, 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.
 
 part of dart.collection;
 
 /**
  * Abstract implementation of a list.
  *
  * All operations are defined in terms of `length`, `operator[]`,
@@ skipping 371 matching lines @@
         this[start + i] = otherList[otherStart + i];
       }
     } else {
       for (int i = 0; i < length; i++) {
         this[start + i] = otherList[otherStart + i];
       }
     }
   }
 
   void replaceRange(int start, int end, Iterable<E> newContents) {
-    // TODO(floitsch): Optimize this.
-    removeRange(start, end);
-    insertAll(start, newContents);
+    _rangeCheck(start, end);
+    if (newContents is! EfficientLength) {
+      newContents = newContents.toList();
+    }
+    int removeLength = end - start;
+    int insertLength = newContents.length;
+    if (removeLength >= insertLength) {
+      int delta = removeLength - insertLength;
+      int insertEnd = start + insertLength;
+      int newLength = this.length - delta;
+      this.setRange(start, insertEnd, newContents);
+      if (delta != 0) {
+        this.setRange(insertEnd, newLength, this, end);
+        this.length = newLength;
+      }
+    } else {
+      int delta = insertLength - removeLength;
+      int newLength = this.length + delta;
+      int insertEnd = start + insertLength;  // aka. end + delta.

[floitsch, 2013/10/10 13:04:53]

No need for comment (imho).

+      this.length = newLength;
+      this.setRange(insertEnd, newLength, this, end);
+      this.setRange(start, insertEnd, newContents);
+    }
   }
 
   int indexOf(Object element, [int startIndex = 0]) {
     if (startIndex >= this.length) {
       return -1;
     }
     if (startIndex < 0) {
       startIndex = 0;
     }
     for (int i = startIndex; i < this.length; i++) {
@@ skipping 49 matching lines @@
     E result = this[index];
     setRange(index, this.length - 1, this, index + 1);
     length--;
     return result;
   }
 
   void insertAll(int index, Iterable<E> iterable) {
     if (index < 0 || index > length) {
       throw new RangeError.range(index, 0, length);
     }
-    // TODO(floitsch): we can probably detect more cases.
-    if (iterable is! List && iterable is! Set && iterable is! SubListIterable) {
+    if (iterable is EfficientLength) {
       iterable = iterable.toList();
     }
     int insertionLength = iterable.length;
     // There might be errors after the length change, in which case the list
     // will end up being modified but the operation not complete. Unless we
     // always go through a "toList" we can't really avoid that.
     this.length += insertionLength;
     setRange(index + insertionLength, this.length, this, index);
     setAll(index, iterable);
   }
@@ skipping 22 matching lines @@
       result.writeAll(this, ', ');
       result.write(']');
      } finally {
        assert(identical(_toStringList.last, this));
        _toStringList.removeLast();
      }
 
     return result.toString();
   }
 }