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

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

Requirements

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

Standard library

All type transformation traits satisfy TransformationTrait.

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)