template_arity.hpp

来自「boost库提供标准的C++ API 配合dev c++使用,功能更加强大」· HPP 代码 · 共 83 行

// preprocessed version of 'boost/mpl/aux_/template_arity.hpp' header
// see the original for copyright information

namespace boost { namespace mpl { namespace aux {

template< int N > struct arity_tag
{
    typedef char (&type)[N + 1];
};

template<
      int C1, int C2, int C3, int C4, int C5
    >
struct max_arity
{
    static int const value =
         ( C5 > 0 ? C5 : ( C4 > 0 ? C4 : ( C3 > 0 ? C3 : ( C2 > 0 ? C2 : ( C1
         > 0 ? C1 : -1 ) ) ) ) )
        ;
};

arity_tag<0> arity_helper(...);

template<
      template< typename P1 > class F
    , typename T1
    >
typename arity_tag<1>::type
arity_helper(type_wrapper< F<T1> >,arity_tag<1 >);

template<
      template< typename P1, typename P2 > class F
    , typename T1, typename T2
    >
typename arity_tag<2>::type
arity_helper(type_wrapper< F<T1,T2> >,arity_tag<2 >);

template<
      template< typename P1, typename P2, typename P3 > class F
    , typename T1, typename T2, typename T3
    >
typename arity_tag<3>::type
arity_helper(type_wrapper< F<T1,T2,T3> >,arity_tag<3 >);

template<
      template< typename P1, typename P2, typename P3, typename P4 > class F
    , typename T1, typename T2, typename T3, typename T4
    >
typename arity_tag<4>::type
arity_helper(type_wrapper< F<T1,T2,T3,T4> >,arity_tag<4 >);

template<
      template<
          typename P1, typename P2, typename P3, typename P4
        , typename P5
        >
      class F
    , typename T1, typename T2, typename T3, typename T4, typename T5
    >
typename arity_tag<5>::type
arity_helper(type_wrapper< F<T1,T2,T3,T4,T5> >,arity_tag<5 >);

template< typename F, int N >
struct template_arity_impl
{
    static int const value =
         sizeof(arity_helper(type_wrapper<F>(),arity_tag<N>())) - 1
        ;
};

template< typename F >
struct template_arity
{
    static int const value =
         ( max_arity< template_arity_impl<F,1 >::value, template_arity_impl<
         F,2 >::value, template_arity_impl< F,3 >::value, template_arity_impl<
         F,4 >::value, template_arity_impl< F,5 >::value >::value )
        ;
};

}}} // namespace boost::mpl::aux