[Bug libstdc++/54388] [4.7/4.8 Regression] std::array.at() const results in undefined behaviour

[bkoz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54388

--- Comment #9 from Benjamin Kosnik <bkoz at gcc dot gnu.org> 2012-08-30 
15:36:18 UTC ---

BTW, we definitely need a comment on  why this particular code is so tricky. 

// NB: Interesting use of comma operator semantics.

at the very least...

;)