[boost] [result_of][patch] decltype-based implementation

From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2008-05-09 12:35:21

Hello,

With all the recent discussion about result_of and now that decltype
has started to trickle into compilers, I thought it might be a good
time for Boost to provide a result_of along the lines of the
typeof-based implementation described in N1454. I've attached a patch
to Ticket #862, which does this.

http://svn.boost.org/trac/boost/ticket/862

This is an old bug report that apparently got a little mangled during
the SVN migration, but I think result_of/lambda compatibility is a
familiar problem. My patch fixes the problem of using result_of with
lambda on compilers that support decltype. It does not preclude fixes
to the problem on C++03 platforms, such as Shunsuke Sogame's Egg and
Marco Costalba's multi-signature function, for example. It also makes
boost::result_of more compliant with the current C++0x std::result_of
described in N2588.

My patch differs from N2588 in that std::result_of only supports
function call expressions of the form f(x). I read this as precluding
support for member function pointers, which are invoked with
expressions of the form o->*f(x). My patch reuses the pointer
specialization from the current implementation, so that
boost::result_of can continue support both. It also may differ from
N2588 in terms of the lvalue/rvalue specifications. I'm not sure that
I understand this correctly, and I would be grateful if someone would
look over it to see if my implementation should be changed for better
conformance.

The patch also includes updates to the documentation and tests. I
tested with msvc 9, gcc 3.4, and gcc 4.3. Thanks for your
consideration!

Daniel Walker