Modern C++ Programming Cookbook

Getting ready

Developers have used a class template usually called enable_if for many years in conjunction with SFINAE to implement constraints on template types. The enable_if family of templates has become part of the C++11 standard and is implemented as follows:

    template<bool Test, class T = void>     struct enable_if     {};     template<class T>     struct enable_if<true, T>     {       typedef T type;     };

To be able to use std::enable_if, you must include the header <type_traits>.