Re: [Boost-users] Testing whether result_of<F(U)> is a valid expression

On 08/02/13 11:12, oswin krause wrote:

Hi,

Is it possible to evaluate, whether a certain argument type given to a functor will lead to a valid expression with the result_of template?

i am trying to achieve the following, maybe there is a better way to do it:

template Container< typename boost::result_of::type > transform( Container<T> c, F f, std::disable_if >::type* dummy = 0

What do you call a valid expression? F(Block<T>) is certainly not an expression. You could test if F::result< F(Block<T>) >::type exists, or whether declval<F>()(declval< Block<T> >()) is a valid expression. Both can be done using SFINAE, the latter will require a recent enough compiler that supports generalized SFINAE (GCC does it since 4.6 I believe).