third_party/boost/type_traits/doc/conditional.qbk

[/ 
  Copyright 2010 John Maddock.
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
]

[/===================================================================]
[section:conditional 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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