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Front Page / Metafunctions / Type Selection / if_c |
Returns one of its two arguments, T1 or T2, depending on the value of integral constant c. if_c<c,t1,t2>::type is a shorcut notation for if_< bool_<c>,t1,t2 >::type.
#include <boost/mpl/if.hpp>
Parameter | Requirement | Description |
---|---|---|
c | An integral constant | A selection condition. |
T1, T2 | Any type | Types to select from. |
For any integral constant c and arbitrary types t1, t2:
typedef if_c<c,t1,t2>::type t;
Return type: | Any type. |
---|---|
Semantics: | Equivalent to typedef if_< bool_<c>,t1,t2 >::type t; |
typedef if_c<true,char,long>::type t1; typedef if_c<false,char,long>::type t2; BOOST_MPL_ASSERT(( is_same<t1, char> )); BOOST_MPL_ASSERT(( is_same<t2, long> ));
// allocates space for an object of class T on heap or "inplace" // depending on its size template< typename T > struct lightweight { // ... typedef typename if_c< sizeof(T) <= sizeof(T*) , inplace_storage<T> , heap_storage<T> >::type impl_t; impl_t impl; };