Synopsis

template< int n > struct arg;
template<> struct arg<1>
{
    template< typename A1,|...| typename An = |unspecified| >
    struct apply
    {
        typedef A1 type;
    };
};
|...|
template<> struct arg<n>
{
    template< typename A1,|...| typename An >
    struct apply
    {
        typedef An type;
    };
};

Description

arg<n> specialization is a |Metafunction Class| that return the nth of its arguments.

Header

#include <boost/mpl/arg.hpp>

Parameters

Expression semantics

For any integral constant n in the range [1, |BOOST_MPL_LIMIT_METAFUNCTION_ARITY|] and arbitrary types |a1...an|:

typedef apply_wrapn< arg<n>,a1,|...|an >::type x;

Example

typedef apply_wrap5< arg<1>,bool,char,short,int,long >::type t1;
typedef apply_wrap5< arg<3>,bool,char,short,int,long >::type t3;
BOOST_MPL_ASSERT(( is_same< t1, bool > ));
BOOST_MPL_ASSERT(( is_same< t3, short > ));

See also

|Composition and Argument Binding|, |Placeholders|, |lambda|, |bind|, |apply|, |apply_wrap|