[boost] [ConceptGCC] for Douglas Gregor

From: Andy Little (andy_at_[hidden])
Date: 2006-10-20 07:54:14

Hi Doulas,

I sent this privately but have a feeling it may have got sopammed out. If you 
got it, apologies for abusing the boost list.

Hi Douglas,

Here is a sample test, but IMO the concept in main should fail, else it is not 
possible to replace a traits class, hence I have had to use one in the 
following:

regards
Andy Little

//-----------------------------//line1
//defines result types for binary ops and for static types with no runtime 
functions
#include <quan/meta/binary_operation.hpp>

namespace quan {namespace meta{

// is a type mpl::void_?
// (binary_operation returns mpl::void for invalid ops, hence the need to 
query )
    namespace detail{

        auto concept NotMplVoid<typename T> {
            typename type = T;
        };

        concept_map NotMplVoid<boost::mpl::void_> {
            typedef void type;
        };
    }

    auto concept IsNotMplVoid< typename T> {
        where std::SameType<detail::NotMplVoid<T>::type,T>;
    };

    auto concept OperatorPlus<typename T1, typename T2>{
        typename type = binary_operation<T1, plus, T2>::type;
        where IsNotMplVoid<type>;
    };

// should I need to do this ?... see below
    template <typename T1, typename T2>
    where OperatorPlus<T1,T2>
    struct operator_plus{
        typedef OperatorPlus<T1,T2>::type type;
    };

}}

#include <quan/meta/rational.hpp>

int main()
{
    using quan::meta::rational;
    // succeeds but shouldnt AFAICS
    // as this is invalid op and type is mpl::void_ here
    typedef quan::meta::OperatorPlus<rational<1>,int >::type res; // line 45

    // fails as expected but why does the Concept version above succeed?
    typedef quan::meta::operator_plus<rational<1>,int >::type res; // line 49
}

ConceptGCC output:

concept_test.cpp: In function 'int main()':
concept_test.cpp:49: error: template arguments for 'struct 
quan::meta::operator_plus<quan::meta::rational<1, 1>, int>' do not meet the 
requirements of the primary template
concept_test.cpp:49: note:   no concept map for requirement 
'quan::meta::OperatorPlus<quan::meta::rational<1, 1>, int>'
concept_test.cpp:49: error: 'type' in class 
'quan::meta::operator_plus<quan::meta::rational<1, 1>, int>' does not name a 
type

ConceptGCC --version:

conceptg++ (GCC) 4.1.1 (Indiana University ConceptGCC alpha 3)
Copyright (C) 2006 Free Software Foundation, Inc.
Copyright (C) 2005, 2006 Trustees of Indiana University.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

regards
Andy Little