Add optional writeAll separator argument.

sdk/lib/core/string_buffer.dart

 // Copyright (c) 2011, 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.core;
 
 /**
  * The StringBuffer class is useful for concatenating strings
  * efficiently. Only on a call to [toString] are the strings
  * concatenated to a single String.
@@ skipping 11 matching lines @@
 
   /** Returns whether the buffer is empty. This is a constant-time operation. */
   bool get isEmpty => length == 0;
 
   /// Adds the contents of [obj], converted to a string, to the buffer.
   external void write(Object obj);
 
   /// Adds the string representation of [charCode] to the buffer.
   external void writeCharCode(int charCode);
 
-  void writeAll(Iterable objects) {
-    for (Object obj in objects) write(obj);
+  void writeAll(Iterable objects, [String separator = ""]) {
+    bool isFirst = true;
+    for (Object obj in objects) {
+      if (isFirst) {
+        isFirst = false;
+      } else {
+        if (separator != "") write(separator);

[sra1, 2013/03/22 21:19:46]

Can we avoid this repeated test in the loop?
Or at least fold it with isFirst:

if (separator == "") separator = null;
String nextSeparator = null;
for (var obj in objects) {
  if (nextSeparator != null) write(nextSeparator);
  nextSeparator = separator;
  write(object);
}

[floitsch, 2013/03/26 18:30:23]

Done.

[Lasse Reichstein Nielsen, 2013/04/03 10:35:52]

If speed is of the essence, I'd prefer:
 void writeAll(Iterable objects, [String separator = ""]) {
   if (separator.isEmpty) {
     for (Object object in objects) {
       write(object);
     }
   } else {
     Iterator iterator = objects.iterator();
     if (!iterator.moveNext()) return;
     write(iterator.current);
     while (iterator.moveNext()) {
       write(separator);
       write(iterator.current);
     }
   }
 }

Or, at least initialize nextSeparator to "" and drop the test completely.

[floitsch, 2013/04/04 22:36:36]

I didn't use Stephen's suggestion but had a code that is pretty similar to
yours. Assuming as "done", but feel free to verify.

+      }
+      write(obj);
+    }
   }
 
   void writeln([Object obj = ""]) {
     write(obj);
     write("\n");
   }
 
   /**
    * Clears the string buffer.
    */
   external void clear();
 
   /// Returns the contents of buffer as a concatenated string.
   external String toString();
 }