avoid extra copy
avoid extra copy

Reviewed By: vitaut

Differential Revision: D23036212

fbshipit-source-id: f370fe5300f5ea28aed7c244ad6c10b089c3e7c3

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift