code review 4625068: io.WriteString: if the object has a WriteString method,...

src/pkg/io/io.go

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Package io provides basic interfaces to I/O primitives.
 // Its primary job is to wrap existing implementations of such primitives,
 // such as those in package os, into shared public interfaces that
 // abstract the functionality, plus some other related primitives.
 package io
 
@@ skipping 191 matching lines @@
 //
 // UnreadRune causes the next call to ReadRune to return the same rune
 // as the previous call to ReadRune.
 // It may be an error to call UnreadRune twice without an intervening
 // call to ReadRune.
 type RuneScanner interface {
         RuneReader
         UnreadRune() os.Error
 }
 
+// stringWriter is the interface that wraps the WriteString method.
+type stringWriter interface {
+        WriteString(s string) (n int, err os.Error)
+}
+
 // WriteString writes the contents of the string s to w, which accepts an array of bytes.
 func WriteString(w Writer, s string) (n int, err os.Error) {
+        if sw, ok := w.(stringWriter); ok {
+                return sw.WriteString(s)
+        }
         return w.Write([]byte(s))
 }
 
 // ReadAtLeast reads from r into buf until it has read at least min bytes.
 // It returns the number of bytes copied and an error if fewer bytes were read.
 // The error is os.EOF only if no bytes were read.
 // If an EOF happens after reading fewer than min bytes,
 // ReadAtLeast returns ErrUnexpectedEOF.
 // If min is greater than the length of buf, ReadAtLeast returns ErrShortBuffer.
 func ReadAtLeast(r Reader, buf []byte, min int) (n int, err os.Error) {
@@ skipping 198 matching lines @@
         }
         off += s.base
         if max := s.limit - off; int64(len(p)) > max {
                 p = p[0:max]
         }
         return s.r.ReadAt(p, off)
 }
 
 // Size returns the size of the section in bytes.
 func (s *SectionReader) Size() int64 { return s.limit - s.base }