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

sdk/lib/_internal/lib/js_string.dart

Index: sdk/lib/_internal/lib/js_string.dart
diff --git a/sdk/lib/_internal/lib/js_string.dart b/sdk/lib/_internal/lib/js_string.dart
index 6482d8bf0dc0c08f8bab289be3b2604cfd66506f..8e99cde8f92f3e9d071087513c60ac6c83f5adfb 100644
--- a/sdk/lib/_internal/lib/js_string.dart
+++ b/sdk/lib/_internal/lib/js_string.dart
@@ -226,20 +226,13 @@ class JSString extends Interceptor implements String, JSIndexable {
     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);
@@ -247,8 +240,7 @@ class JSString extends Interceptor implements String, JSIndexable {
     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);