std::experimental::void_t - cppreference.com

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

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 and the LFTS v2 is based on C++14.

See also