Add StringSink and update StringBuffer.

sdk/lib/core/string_buffer.dart

Index: sdk/lib/core/string_buffer.dart
diff --git a/sdk/lib/core/string_buffer.dart b/sdk/lib/core/string_buffer.dart
index d8b393583952238a7e66027ba20d0b45b86179e4..4a1ed4763a35fd41aa560dbc559e6cd7f7799202 100644
--- a/sdk/lib/core/string_buffer.dart
+++ b/sdk/lib/core/string_buffer.dart
@@ -9,29 +9,73 @@ part of dart.core;
  * efficiently. Only on a call to [toString] are the strings
  * concatenated to a single String.
  */
-abstract class StringBuffer {
+class StringBuffer implements StringSink {
 
   /// Creates the string buffer with an initial content.
-  external factory StringBuffer([Object content = ""]);
+  StringBuffer([Object content = ""]) {

[Lasse Reichstein Nielsen, 2013/02/11 12:30:11]

Just make the constructor external.

[floitsch, 2013/02/11 17:10:49]

Done.

+    // TODO(floitsch): remove or rewrite this call to clear. It is currently
+    // necessary because the VM doesn't allow default values for fields in
+    // patch classes.
+    clear();
+    write(content);
+  }
 
   /// Returns the length of the buffer.
-  int get length;
+  external int get length;
 
-  // Returns whether the buffer is empty.
-  bool get isEmpty;
+  /// Returns whether the buffer is empty.
+  bool get isEmpty => length == 0;
 
-  /// Converts [obj] to a string and adds it to the buffer.
-  void add(Object obj);
+  /**
+   * Converts [obj] to a string and adds it to the buffer.
+   *
+   * *Deprecated*. Use [write] instead.
+   */
+  @deprecated
+  void add(Object obj) => write(obj);
+
+  void write(Object obj) {
+    // TODO(srdjan): The following four lines could be replaced by
+    // '$obj', but apparently this is too slow on the Dart VM.
+    String str = obj.toString();
+    if (str is! String) {
+      throw new ArgumentError('toString() did not return a string');
+    }
+    if (str.isEmpty) return;
+    _write(str);
+  }
+
+
+  void print(Object obj) {
+    write(obj);
+    write("\n");

[Lasse Reichstein Nielsen, 2013/02/11 12:30:11]

_write for the second call.

[floitsch, 2013/02/11 17:10:49]

Done.

+  }
 
   /// Adds the string representation of [charCode] to the buffer.
-  void addCharCode(int charCode);
+  void addCharCode(int charCode) {
+    write(new String.fromCharCode(charCode));

[Lasse Reichstein Nielsen, 2013/02/11 12:30:11]

_write

[floitsch, 2013/02/11 17:10:49]

Done.

+  }
 
-  /// Adds all items in [objects] to the buffer.
-  void addAll(Iterable objects);
+  /**
+   * Adds all items in [objects] to the buffer.
+   *
+   * *Deprecated*. Use `objects.forEach(buffer.write)` instead.

[Lasse Reichstein Nielsen, 2013/02/11 12:30:11]

Backquotes are not part of the dartdoc spec. Use [::] instead.

[floitsch, 2013/02/11 17:10:49]

Done.

+   */
+  @deprecated

[floitsch, 2013/02/09 00:59:02]

Not sure about this.

[Lasse Reichstein Nielsen, 2013/02/11 12:30:11]

Agree, I'd vote for removing it.
Let the iterable do the iteration, not us.

+  void addAll(Iterable objects) {
+    for (Object obj in objects) write(obj);
+  }
 
-  /// Clears the string buffer.
-  void clear();
+  /**
+   * Clears the string buffer.
+   *
+   * *Deprecated*.
+   */
+  @deprecated

[floitsch, 2013/02/09 00:59:02]

Not sure about this.

[Lasse Reichstein Nielsen, 2013/02/11 12:30:11]

I'm not sure we should have a clear method at all.
It's better to just create a new sink if you need it.
Having a destructive operation like this on an object you might want to pass to
other code isn't safe.

If we have it, how about giving it an optional position argument, so you can
reset to any previous length.

[floitsch, 2013/02/11 17:10:49]

Let's deprecate it then.

+  external void clear();
 
   /// Returns the contents of buffer as a concatenated string.
-  String toString();
+  external String toString();
+
+  external void _write(String str);
 }