Summary:
I was watching a classic magnificent talk about modern C++ by Herb Sutter and I was totally sold on double down on using `auto` in our codebase. Surprisingly, 95% of the code base already follows Herb's guidence; I just changed the last 5% to make it consistent.
All those changes must work *exactly* like it was before.
The talk: https://youtu.be/xnqTKD8uD64?t=28m25s
Reviewed By: mdvacca
Differential Revision: D9753301
fbshipit-source-id: 9629aa485a5d6e51806cc96306c297284d4f90b8
9570d7d490