libcore: Make BytesWriters not require shared boxes.

src/libcore/io.rs

@@ -687,7 +687,7 @@ struct BytesWriter {
     mut pos: uint,
 }
 
-impl @BytesWriter: Writer {
+impl BytesWriter: Writer {
     fn write(v: &[const u8]) {
         do self.buf.swap |buf| {
             let mut buf <- buf;
@@ -716,12 +716,20 @@ fn flush() -> int { 0 }
     fn get_type() -> WriterType { File }
 }
 
-fn BytesWriter() -> @BytesWriter {
-    @BytesWriter { buf: DVec(), mut pos: 0u }
+impl @BytesWriter : Writer {
+    fn write(v: &[const u8]) { (*self).write(v) }
+    fn seek(offset: int, whence: SeekStyle) { (*self).seek(offset, whence) }
+    fn tell() -> uint { (*self).tell() }
+    fn flush() -> int { (*self).flush() }
+    fn get_type() -> WriterType { (*self).get_type() }
+}
+
+fn BytesWriter() -> BytesWriter {
+    BytesWriter { buf: DVec(), mut pos: 0u }
 }
 
 fn with_bytes_writer(f: fn(Writer)) -> ~[u8] {
-    let wr = BytesWriter();
+    let wr = @BytesWriter();
     f(wr as Writer);
     wr.buf.check_out(|buf| buf)
 }

src/rustc/metadata/encoder.rs

@@ -1093,7 +1093,7 @@ fn encode_hash(ebml_w: ebml::Writer, hash: ~str) {
                                             0, 0, 0, 1 ];
 
 fn encode_metadata(parms: encode_parms, crate: @crate) -> ~[u8] {
-    let wr = io::BytesWriter();
+    let wr = @io::BytesWriter();
     let stats =
         {mut inline_bytes: 0,
          mut attr_bytes: 0,