encoding/json: RawMessage should marshal without pointer receiver

[augustoroman]

The current json.RawMessage implementation defines MarshalJSON on a pointer receiver. 
This causes unexpected behavior when marshalling with non-pointer-receiver objects.

For example:
http://play.golang.org/p/Cf_6zpIKC0

Instead, MarshalJSON should be defined on a non-pointer receiver for json.RawMessage. 
This will continue to work for existing code that uses pointer-receivers, but will
change behavior to work "correctly" on code that accidentally uses
non-pointer-receivers.

[robpike]

Comment 1:

Can't be changed but worth documenting.

Labels changed: added priority-later, documentation, removed priority-triage.

Status changed to Accepted.

[gopherbot]

Comment 2 by mattyjwilliams:

What's the solution here? Adding a comment to
http://golang.org/src/pkg/encoding/json/stream.go?s=4434:4484#L175 to warn that calling
json.Marshal on a non-pointer json.RawMessage can return "meaningless" data with err ==
nil

[rsc]

Comment 3:

Labels changed: added go1.3maybe.

[rsc]

Comment 5:

Labels changed: added release-none, removed go1.3maybe.

[rsc]

Comment 6:

Labels changed: added repo-main.