| Front Page / Metafunctions / Type Selection / eval_if |
template<
typename C
, typename F1
, typename F2
>
struct eval_if
{
typedef unspecified type;
};
Evaluates one of its two nullary-metafunction arguments, F1 or F2, depending on the value C.
#include <boost/mpl/eval_if.hpp>
| Parameter | Requirement | Description |
|---|---|---|
| C | Integral Constant | An evaluation condition. |
| F1, F2 | Nullary Metafunction | Metafunctions to select for evaluation from. |
For any Integral Constant c and nullary Metafunctions f1, f2:
typedef eval_if<c,f1,f2>::type t;
| Return type: | Any type. |
|---|---|
| Semantics: | If c::value == true, t is identical to f1::type; otherwise t is identical to f2::type. |