Allow multi-codeunit padding in String.padLeft/padRight.

sdk/lib/_internal/lib/js_string.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.
 
 part of _interceptors;
 
 /**
  * The interceptor class for [String]. The compiler recognizes this
  * class as an interceptor, and changes references to [:this:] to
  * actually use the receiver of the method, which is generated as an extra
@@ skipping 208 matching lines @@
           endIndex--;
         } else {
           break;
         }
       }
     }
     if (startIndex == 0 && endIndex == result.length) return result;
     return JS('String', r'#.substring(#, #)', result, startIndex, endIndex);
   }
 
-  String repeat(int times, [String separator = ""]) {
-    if (times < 0) throw new RangeError.value(times);
-    if (times == 0) return "";
-    if (separator.isEmpty) {
-      return JS('String', "new Array(# + 1).join(#)", times, this);
-    } else {
-      var list = new JSArray.growable(times);
-      for (int i = 0; i < times; i++) list[i] = this;
-      return JS('String', "#.join(#)", list, separator);
-    }
+  String operator*(int times) {
+    if (times <= 0) return "";
+    if (times == 1) return this;
+    return JS('String', "new Array(# + 1).join(#)", times, this);

[sra1, 2014/02/19 21:18:09]

I'm a bit nervous of this idiom (in all three places).

AFAIK from looking at the V8 code, join is only optimized for lists of ascii
strings, which this is not.  I think you end up with another temporary
allocation here to hold the stringified elements:
https://code.google.com/p/v8/codesearch#v8/trunk/src/array.js&l=147

Some kind of length-doubling algorithm is likely to work well.

[Lasse Reichstein Nielsen, 2014/02/20 07:16:40]

I've incorporated your CL, so all this goes away.

   }
 
-  String padLeft(int newLength, String padding) {
-    if (padding.length != 1) throw new ArgumentError(padding);
+  String padLeft(int newLength, [String padding = ' ']) {
     int delta = newLength - this.length;
     if (delta <= 0) return this;
     var list = new JSArray.growable(delta + 1);
     list[delta] = this;

[sra1, 2014/02/19 21:18:09]

Current range analysis does not seem to eliminate this bounds check.

     return JS("String", "#.join(#)", list, padding);

[sra1, 2014/02/19 21:18:09]

Single quotes to match the rest of the file.

   }
 
-  String padRight(int newLength, String padding) {
-    if (padding.length != 1) throw new ArgumentError(padding);
+  String padRight(int newLength, [String padding = ' ']) {
     int delta = newLength - this.length;
     if (delta <= 0) return this;
     var list = new JSArray.growable(delta + 1);
     list[0] = this;
     return JS("String", "#.join(#)", list, padding);
   }
 
   List<int> get codeUnits => new _CodeUnits(this);
 
   Runes get runes => new Runes(this);
@@ skipping 97 matching lines @@
  */
 class _CodeUnits extends UnmodifiableListBase<int> {
   /** The string that this is the code units of. */
   String _string;
 
   _CodeUnits(this._string);
 
   int get length => _string.length;
   int operator[](int i) => _string.codeUnitAt(i);
 }