> I'm a user, but I've never seen a usage like this before.
So this snippet comes from a sizable code base. Took a long time to pinpoint then distill the issue down to the 6-line example! Pretty sure that std::bind / std::function don't support this usage, or at least it didn't work when I tried for a few minutes. Boost flavor seems a bit more featured.
The actual offender is the bigger change in bind/bind.hpp from 1.59 to 1.60 (not the trivial changes in args or placeholder). I can see they added significant std::forward / rvalue support. If I set
BOOST_NO_CXX11_RVALUE_REFERENCES then also it continues to work. I suspect we've hit a corner case issue with forward / rvalue and boost::function / boost::shared_ptr.