Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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conditional

Header: #include <boost/type_traits/conditional.hpp> or #include <boost/type_traits.hpp>

namespace boost {
  template <bool B, class T, class U>  struct conditional;
  template <bool B, class T, class U>  using conditional_t = typename conditional<B, T, U>::type; // C++11 and above
}

If B is true, the member typedef type shall equal T. If B is false, the member typedef type shall equal U.


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