code review 166041: Add ReadFrom and WriteTo methods to bytes.Buffer, to en...

Add ReadFrom and WriteTo methods to bytes.Buffer, to enable i/o without buffer allocation.
Use them in Copy and Copyn.
Speed up ReadFile by using ReadFrom and avoiding Copy altogether (a minor win).

[r, 2009-12-03 19:21:12]

Hello rsc, gri (cc: golang-dev@googlegroups.com),

I'd like you to review the following change.

[rsc, 2009-12-03 20:44:40]

LGTM

http://codereview.appspot.com/166041/diff/1001/1002
File src/pkg/bytes/buffer.go (right):

http://codereview.appspot.com/166041/diff/1001/1002#newcode96
src/pkg/bytes/buffer.go:96: // Buffer.ReadFrom.  As long as the Buffer has at
least MinRead unused bytes,
As long as the Buffer has at least MinRead bytes beyond
what is required to hold the contents of r, ReadFrom will
not grow the buffer.

http://codereview.appspot.com/166041/diff/1001/1002#newcode130
src/pkg/bytes/buffer.go:130: return n, nil;	// err may be EOF, so return nil
explicitly
s/may be/is/

http://codereview.appspot.com/166041/diff/1001/1004
File src/pkg/io/io.go (right):

http://codereview.appspot.com/166041/diff/1001/1004#newcode190
src/pkg/io/io.go:190: // It returns the number of bytes copied and the error, if
any.
//
// If dst implements the ReaderFrom interface,
// the copy is implemented by calling dst.ReadFrom.

http://codereview.appspot.com/166041/diff/1001/1004#newcode228
src/pkg/io/io.go:228: // copied and the error, if any.
//
// If dst implements the ReaderFrom interface,
// the copy is implemented by calling dst.ReadFrom(src).
// If src implements the WriterTo interface,
// the copy is implemented by calling src.WriteTo(dst).

http://codereview.appspot.com/166041/diff/1001/1004#newcode231
src/pkg/io/io.go:231: // Avoids an allocation.
d
(avoids the copy too; probably not necessary to say)

http://codereview.appspot.com/166041/diff/1001/1005
File src/pkg/io/io_test.go (right):

http://codereview.appspot.com/166041/diff/1001/1005#newcode15
src/pkg/io/io_test.go:15: // An implementation of Read and Write but not
ReadFrom and WriteTo
type Buffer {
    bytes.Buffer;
    io.ReaderFrom;  // conflict with Buffer.ReadFrom
    io.WriterTo;  // conflict with Buffer.WriteTo
}

[r, 2009-12-03 20:56:18]

*** Submitted as http://code.google.com/p/go/source/detail?r=27508885c08d ***

Add ReadFrom and WriteTo methods to bytes.Buffer, to enable i/o without buffer
allocation.
Use them in Copy and Copyn.
Speed up ReadFile by using ReadFrom and avoiding Copy altogether (a minor win).

R=rsc, gri
CC=golang-dev
http://codereview.appspot.com/166041