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3rdparty/boost_1_81_0/boost/compute/functional/get.hpp 1.84 KB
63e88f80   Hu Chunming   提交三方库
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  //---------------------------------------------------------------------------//
  // Copyright (c) 2013 Kyle Lutz <kyle.r.lutz@gmail.com>
  //
  // 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
  //
  // See http://boostorg.github.com/compute for more information.
  //---------------------------------------------------------------------------//
  
  #ifndef BOOST_COMPUTE_FUNCTIONAL_GET_HPP
  #define BOOST_COMPUTE_FUNCTIONAL_GET_HPP
  
  #include <cstddef>
  
  #include <boost/compute/types/fundamental.hpp>
  #include <boost/compute/type_traits/scalar_type.hpp>
  
  namespace boost {
  namespace compute {
  namespace detail {
  
  // meta-function returning the result type for get<N>()
  template<size_t N, class Arg>
  struct get_result_type
  {
      typedef typename scalar_type<Arg>::type type;
  };
  
  template<size_t N, class Arg, class T>
  struct invoked_get
  {
      typedef typename get_result_type<N, T>::type result_type;
  
      invoked_get(const Arg &arg)
          : m_arg(arg)
      {
      }
  
      Arg m_arg;
  };
  
  } // end detail namespace
  
  /// Returns the \c N'th element of an aggregate type (e.g. scalarN,
  /// pair, tuple, etc.).
  ///
  /// \see \ref field "field<T>"
  template<size_t N>
  struct get
  {
      /// \internal_
      template<class> struct result;
  
      /// \internal_
      template<class F, class Arg>
      struct result<F(Arg)>
      {
          typedef typename detail::get_result_type<N, Arg>::type type;
      };
  
      template<class Arg>
      detail::invoked_get<
          N, Arg, typename boost::remove_cv<typename Arg::result_type>::type
      > operator()(const Arg &arg) const
      {
          typedef typename boost::remove_cv<typename Arg::result_type>::type T;
  
          return detail::invoked_get<N, Arg, T>(arg);
      }
  };
  
  } // end compute namespace
  } // end boost namespace
  
  #endif // BOOST_COMPUTE_FUNCTIONAL_GET_HPP