Call special VM interpolate for single element interpolation.

runtime/lib/string_patch.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.
 
 patch class String {
   /* patch */ factory String.fromCharCodes(Iterable<int> charCodes) {
     return _StringBase.createFromCharCodes(charCodes);
   }
 
   /* patch */ factory String.fromCharCode(int charCode) {
@@ skipping 500 matching lines @@
     int startIndex = 0;
     for (Match match in pattern.allMatches(this)) {
       buffer.write(onNonMatch(this.substring(startIndex, match.start)));
       buffer.write(onMatch(match).toString());
       startIndex = match.end;
     }
     buffer.write(onNonMatch(this.substring(startIndex)));
     return buffer.toString();
   }
 
+  // Convert single object to string.
+  static String _interpolateSingle(final Object o) {

[Florian Schneider, 2014/09/12 10:33:37]

final is not really necessary here.

[Lasse Reichstein Nielsen, 2014/09/12 12:49:38]

Done.

+    final s = o.toString();
+    if (s is! String) {
+      throw new ArgumentError(o);
+    }
+    return s;
+  }
 
   /**
    * Convert all objects in [values] to strings and concat them
    * into a result string.
    */
   static String _interpolate(List<String> values) {
     final numValues = values.length;
     _List stringList = new List<String>(numValues);
     bool isOneByteString = true;
     int totalLength = 0;
@@ skipping 479 matching lines @@
 class _CodeUnits extends Object with ListMixin<int>,
                                      UnmodifiableListMixin<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);
 }