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

Jeffrey Lee Hellrung, Jr. wrote:

On Sun, Apr 21, 2013 at 7:48 AM, Daniel Walker wrote:

...

This is due to a dark corner of TR1: the result and result_type members are consulted in non-nullary functors but nullary functors always generate void. (See the section on known difference between boost::result_of and TR1 in the documentation.)

The rationale for this always confused me, with the end result (it seems) that it makes TR1 result_of basically unusable for nullary function calls.

result_type is consulted. result<> is not. type is void (instead of a compile error) when there is no result_type. The reason for the type being void is that in template<class T> class reference_wrapper { private: T & t_; public: typename result_of::type operator()() const { return t_(); } }; operator()() is not a template. If result_of::type wasn't present or generated an error when T doesn't have result<>, reference_wrapper<int> would have generated an error when instantiated. In C++11, you can make operator()() a template. In C++03, you can't.