From: Andy Little (andy_at_[hidden])
Date: 2006-07-25 06:42:04
"Andy Little" <andy_at_[hidden]> wrote in message
news:ea4hqs$lg0$1_at_sea.gmane.org...
Further the following code should work AFAICS, at least according to the
documentation
#include <boost/mpl/equal_to.hpp>
#include <boost/mpl/integral_c.hpp>
#include <boost/mpl/next.hpp>
#include <boost/mpl/prior.hpp>
#include <boost/mpl/assert.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/static_assert.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/mpl/int.hpp>
#include <boost/mpl/integral_c.hpp>
#include <iostream>
// Write a type fulfilling the Integral Constant requirements
// http://www.boost.org/libs/mpl/doc/refmanual/integral-constant.html
template <int N>
struct my_int{
typedef int value_type;
static const int value = N;
operator int ()const { return value;}
typedef my_int type;
};
namespace boost{ namespace mpl{
template <int N >
struct next<my_int<N> > {
typedef my_int<N+1> type;
};
template <int N >
struct prior<my_int<N> > {
typedef my_int<N-1> type;
};
}}
/*
Check a type is a model of Integral Constant
http://www.boost.org/libs/mpl/doc/refmanual/integral-constant.html
*/
template <typename T>
void IntegralConstantConcept()
{
typedef typename boost::mpl::next<T>::type next_type;
typedef typename boost::mpl::prior<T>::type prior_type;
typedef typename T::type type;
typedef typename T::value_type value_type;
typename T::value_type t = T::value;
typename T::value_type t1 = T();
static int const next_value = T::value +1;
static int const prior_value = T::value -1;
BOOST_MPL_ASSERT( (boost::is_same<type,T>) );
BOOST_STATIC_ASSERT( (next_type::value == next_value));
BOOST_STATIC_ASSERT( (prior_type::value == prior_value));
std::cout << typeid (T).name() << "passed Integral Concept Concept
Check\n";
};
namespace mpl = boost::mpl;
int main()
{
// Concept check
IntegralConstantConcept<my_int<1> >();
IntegralConstantConcept<mpl::integral_c<int,1> >();
IntegralConstantConcept<mpl::int_<1> >();
// fails
// IntegralConstantConcept<mpl::bool_<true> >();
// should fail
// IntegralConstantConcept<int >();
// Should work !
// http://www.boost.org/libs/mpl/doc/refmanual/equal-to.html
bool result = mpl::equal_to< my_int<1>,my_int<1> >::value ;
std::cout << result << '\n';
}
regards
Andy Little