std::experimental::void_t

From cppreference.com
Defined in header <experimental/type_traits>
template< class... >
using void_t = void;
(library fundamentals TS v2)

A utility metafunction that maps a sequence of any types to the type void.

[edit] Notes

This utility metafunction is used in template metaprogramming to detect ill-formed types in SFINAE context. First voted into C++17 as std::void_t, it was later added as well to the library fundamentals TS as std::experimental::void_t, because it is a dependency of the detection idiom.

[edit] See also

(C++17)
void variadic alias template
(alias template)