...one of the most highly
regarded and expertly designed C++ library projects in the
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— Herb Sutter and Andrei
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Coding Standards
Front Page / Metafunctions / Type Selection / if_ |
template< typename C , typename T1 , typename T2 > struct if_ { typedef unspecified type; };
Returns one of its two arguments, T1 or T2, depending on the value C.
#include <boost/mpl/if.hpp>
Parameter | Requirement | Description |
---|---|---|
C | 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,t1,t2>::type t;
Return type: | Any type. |
---|---|
Semantics: | If c::value == true, t is identical to t1; otherwise t is identical to t2. |
typedef if_<true_,char,long>::type t1; typedef if_<false_,char,long>::type t2; BOOST_MPL_ASSERT(( is_same<t1, char> )); BOOST_MPL_ASSERT(( is_same<t2, long> ));