Expression semantics
typedef op_tag<x>::type tag;
| Semantics: | tag is a tag type for x for op.
tag::value is x's conversion rank. |
|---|
typedef op_impl<
op_tag<x>::type
, op_tag<y>::type
>::apply<x,y>::type r;
| Semantics: | r is the result of op application on arguments x
and y. |
|---|
typedef op<|x1...xn|>::type r;
| Semantics: | r is the result of op application on arguments |x1...xn|. |
|---|
Example
struct complex_tag : int_<10> {};
template< typename Re, typename Im > struct complex
{
typedef complex_tag tag;
typedef complex type;
typedef Re real;
typedef Im imag;
};
template< typename C > struct real : C::real {};
template< typename C > struct imag : C::imag {};
namespace boost { namespace mpl {
template<>
struct plus_impl< complex_tag,complex_tag >
{
template< typename N1, typename N2 > struct apply
: complex<
plus< typename N1::real, typename N2::real >
, plus< typename N1::imag, typename N2::imag >
>
{
};
};
}}
typedef complex< int_<5>, int_<-1> > c1;
typedef complex< int_<-5>, int_<1> > c2;
typedef plus<c1,c2> r1;
BOOST_MPL_ASSERT_RELATION( real<r1>::value, ==, 0 );
BOOST_MPL_ASSERT_RELATION( imag<r1>::value, ==, 0 );
typedef plus<c1,c1> r2;
BOOST_MPL_ASSERT_RELATION( real<r2>::value, ==, 10 );
BOOST_MPL_ASSERT_RELATION( imag<r2>::value, ==, -2 );
typedef plus<c2,c2> r3;
BOOST_MPL_ASSERT_RELATION( real<r3>::value, ==, -10 );
BOOST_MPL_ASSERT_RELATION( imag<r3>::value, ==, 2 );
