eval_if_c

Synopsis

template< 
      bool c
    , typename F1
    , typename F2
    >
struct eval_if_c
{
    typedef unspecified type;
};

Evaluates one of its two nullary-metafunction arguments, F1 or F2, depending on the value of integral constant c. eval_if_c<c,f1,f2>::type is a shorcut notation for eval_if< bool_<c>,f1,f2 >::type.

Header

#include <boost/mpl/eval_if.hpp>

Parameters

Parameter	Requirement	Description
`c`	An integral constant	An evaluation condition.
`F1`, `F2`	Nullary Metafunction	Metafunctions to select for evaluation from.

Expression semantics

For any integral constant c and nullary Metafunctions f1, f2:

typedef eval_if_c<c,f1,f2>::type t;

Return type:	Any type.
Semantics:	Equivalent to `typedef eval_if< bool_<c>,f1,f2 >::type t;`

Example

typedef eval_if_c< true, identity<char>, identity<long> >::type t1;
typedef eval_if_c< false, identity<char>, identity<long> >::type t2;

BOOST_MPL_ASSERT(( is_same<t1,char> ));
BOOST_MPL_ASSERT(( is_same<t2,long> ));