Daniel Walker wrote:
Not a small number of people have complained about the disability of std/boost::result_of for SFINAE.
Where has this come up before? I just don't remember. It would be interesting to know the history of this problem.
I learned this problem from this blog post: (Note: written in Japanese http://d.hatena.ne.jp/gintenlabo/20110420/1303288950 ) This post listed defects in FDIS. One of them is that some meta-functions (std::result_of and common_type) cannot be used for SFINAE. On gcc bugzilla, Paolo Carlini said the following ( http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50711 ) Unfortunately, I don't think you can use std::result_of for sfinae purposes, if I understand correctly it's a well know annoyance which you have to overcome by open coding with std::declval. Eg, if you simply open the <functional> header you will find plenty of decltype( std::declval... for sfinae, which cannot be replaced by a concise std::result_of Also, quick google finds an old boost-user ML post: ( http://thread.gmane.org/gmane.comp.lib.boost.user/9967/focus=10030 ) From: Ian McCulloch Subject: Re: result_of tutorial Date: 2005-03-17 08:22:29 GMT Thanks Peter, I think I understand how it works now. Unfortunately, the lack of SFINAE is a real showstopper for me. I want to write functions like template <typename T> typename result_of<negate(T)>::type operator-(T const& x) { return negate()(x); } but the lack of SFINAE here makes boost::result_of essentially useless for this. But I imagine it won't be difficult to make a new version based on boost that would work. Regards, Michel