[Core] Optimize List

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;
 
 /** A reusable set used to identify cyclic lists during toString() calls. */
 Set _toStringVisiting = new HashSet.identity();
 
 /**
@@ skipping 63 matching lines @@
   }
 
   E get single {
     if (length == 0) throw new StateError("No elements");
     if (length > 1) throw new StateError("Too many elements");
     return this[0];
   }
 
   bool contains(Object element) {
     int length = this.length;
-    for (int i = 0; i < length; i++) {
+    for (int i = 0; i < this.length; i++) {
       if (this[i] == element) return true;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     return false;
   }
 
   bool every(bool test(E element)) {
     int length = this.length;
@@ skipping 58 matching lines @@
       }
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     if (matchFound) return match;
     throw new StateError("No matching element");
   }
 
   String join([String separator = ""]) {
-    int length = this.length;
-    if (!separator.isEmpty) {
-      if (length == 0) return "";
-      String first = "${this[0]}";
-      if (length != this.length) {
-        throw new ConcurrentModificationError(this);
-      }
-      StringBuffer buffer = new StringBuffer(first);
-      for (int i = 1; i < length; i++) {
-        buffer.write(separator);
-        buffer.write(this[i]);
-        if (length != this.length) {
-          throw new ConcurrentModificationError(this);
-        }
-      }
-      return buffer.toString();
+    if (this.length == 0) return "";
+    StringBuffer buffer = new StringBuffer();
+    if (separator.isEmpty) {

[Lasse Reichstein Nielsen, 2014/02/05 10:41:00]

Just checked the StringBuffer code: This "if" isn't necessary, you can just pass
the separator directly to writeAll in all cases.
(It starts by checking if separator.isEmpty itself, and has "" as default too).

[vicb, 2014/02/06 12:42:22]

Indeed. Thank for the tip.

+      buffer.writeAll(this);
     } else {
-      StringBuffer buffer = new StringBuffer();
-      for (int i = 0; i < length; i++) {
-        buffer.write(this[i]);
-        if (length != this.length) {
-          throw new ConcurrentModificationError(this);
-        }
-      }
-      return buffer.toString();
+      buffer.writeAll(this, separator);
     }
+    return buffer.toString();
   }
 
   Iterable<E> where(bool test(E element)) => new WhereIterable<E>(this, test);
 
   Iterable map(f(E element)) => new MappedListIterable(this, f);
 
   Iterable expand(Iterable f(E element)) =>
       new ExpandIterable<E, dynamic>(this, f);
 
   E reduce(E combine(E previousValue, E element)) {
@@ skipping 336 matching lines @@
       result.write('[');
       result.writeAll(this, ', ');
       result.write(']');
      } finally {
        _toStringVisiting.remove(this);
      }
 
     return result.toString();
   }
 }