C++ named requirements: TransformationTrait (since C++11)

A TransformationTrait is a class template that provides a transformation of its template type parameter.

Takes one template type parameter (additional template parameters are optional and allowed).
The transformed type is a publicly accessible nested type named type.

The following standard library class templates also satisfy TransformationTrait.

std::tuple_element<std::tuple> (C++11)	obtains the type of the specified element (class template specialization)
std::tuple_element<std::pair> (C++11)	obtains the type of the elements of `pair` (class template specialization)
std::tuple_element<std::array> (C++11)	obtains the type of the elements of `array` (class template specialization)
variant_alternativevariant_alternative_t (C++17)	obtains the type of the alternative specified by its index, at compile time (class template) (alias template)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/cpp/named_req/TransformationTrait