models_directly.hpp

#ifndef PASTELSYS_MODELS_DIRECTLY_HPP
#define PASTELSYS_MODELS_DIRECTLY_HPP

#include "pastel/sys/concept/models_directly.h"
#include "pastel/sys/type_traits/compiles.h"
#include "pastel/sys/type_traits/remove_cvref.h"

#include <type_traits>

namespace Pastel
{

    template <
        typename Type, 
        typename Concept>
    struct Models_Directly
    {
        // The concept is not in functional form.
        // Convert it to such, assuming no parameters.
        static constexpr bool value = 
            Models_Directly<Type, Concept()>::value;
    };

    template <
        typename Type,
        typename Concept,
        typename... ParameterSet>
    struct Models_Directly<Type, Concept(ParameterSet...)>
    {
    private:
        // Type models Concept if it is possible to call
        // the requires_() member function of Concept.
        // The concept is always given non-const, non-volatile,
        // non-reference arguments to work with, no matter what 
        // the passed-in types are.
        template <
            typename T,
            typename =
                decltype(
                    std::declval<Concept>().requires_(
                        std::declval<
                            RemoveCvRef<T>
                        >(), 
                        std::declval<
                            ParameterSet
                        >()...
                    )
                )
        >
        struct Test
        {
            // The class needs to be defined here ({};); otherwise 
            // it triggers a bug in Visual Studio 2015 RC.
        };

    public:
        static constexpr bool value =
            Compiles<Test, Type>::value;
    };

}

#endif