[Bug c++/24702] Koenig found functoid ref, but "cannot be used as a function"

[pierhyth at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24702

--- Comment #9 from Mark Phillips <pierhyth at gmail dot com> ---
Thanks Jonathan for the information on the updated standard and the rationale
behind restricting Koenig to actual functions and function templates.

In one way it is a bit of a pity - it does make functors second-class citizens
compared to functions - but the linked document explains some additional
considerations, namely the risk of over-visibility of names.  Perhaps it is a
reasonable choice for now.  Hopefully a better solution will be introduced down
the track (maybe extending it to functors, while at the same time
narrowing/allowing-control-over namespaces to be looked up).