Re: [boost] [result_of] Allow result_of to work with C++11 lambdas

On 10/04/13 19:43, Nathan Crookston wrote:

Hi Mathias,

Mathias Gaunard wrote:

...

I personally have my own implementation of result_of which does this. My implementation is also simpler, compiles faster, is optionally optimized for compilers with variadic templates (also supports compilers with decltype but no variadic templates), has preprocessing support, and has the added benefit that result_of<Sig>::type is only defined if Sig is callable.

Sounds pretty slick. Is this in NT2, or just in some other code you have?

Yes. I've found that boost::result_of is often a performance bottleneck. Unfortunately the code in Boost is not as simple as it could be; it instantiates way too many templates, I suppose for legacy purposes. My version could probably still be improved too.

Just so it's clear to others on the list, boost::result_of (at least in trunk) also has result_of<Sig>::type that is only defined when Sig is callable. I believe Eric Niebler added that a while back.

Doesn't work with latest trunk. The code below doesn't compile. /home/mgaunard/dev/boost/trunk/boost/utility/result_of.hpp:173:8: error: no class template named ‘result’ in ‘struct foo’ It does work, however, if instructed to use decltype. My version applies SFINAE in C++03 and without SFINAE for expressions too. #include #include <iostream> struct foo {}; template<class T> typename boost::result_of::type bar(T const& t); void bar(...) { std::cout << "not callable" << std::endl; } int main() { bar(foo()); }