RE: [boost] MPL::lambda on MSVC

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2003-03-30 19:45:44

Jaap Suter wrote:
> Hi,

Hi Jaap,

> 
> I apologize, but once again I'm unable to get a lambda 
> expression working with the MPL.
> 
> The code works fine with the Intel and GCC compiler. On MSVC I get the
> following error:
> 
>     error C2039: 'lhs_index' : is not a member of 'boost::mpl::arg<N>'

It's the same problem we dealt with here -
http://lists.boost.org/MailArchives/boost/msg41700.php. The easiest way to
fix it within the current code base would be this:

template< typename T > struct lhs_index_impl
    : T::lhs_index
{
};

template< typename T > struct lhs_index
    : mpl::if_<
          mpl::is_placeholder<T>
        , T
        , lhs_index_impl<T>
        >
{
    BOOST_MPL_AUX_LAMBDA_SUPPORT(1,lhs_index,(T))
};

template< typename T > struct rhs_index_impl
    : T::rhs_index
{
};

template< typename T > struct rhs_index
    : mpl::if_<
          mpl::is_placeholder<T>
        , T
        , rhs_index_impl<T>
        >
{
    BOOST_MPL_AUX_LAMBDA_SUPPORT(1,rhs_index,(T))
};

template < class Signature, class LhsIndex, class RhsIndex >
struct predicate
{
    typedef typename mpl::and_<
        typename mpl::equal_to<
            typename lhs_index<Signature>::type, LhsIndex
        >::type,
        typename mpl::equal_to<
            typename rhs_index<Signature>::type, RhsIndex
        >::type
    >::type type;

    BOOST_MPL_AUX_LAMBDA_SUPPORT( 3,
        predicate, (Signature, LhsIndex, RhsIndex) )
};

 // Test code:

 typedef mpl::vector< signature< 1, 1, 1 >,
                                 signature< 4, 4, 0 >,
                                 signature< 5, 5, 0 >,
                                 signature< 4, 5, 1 > > signatures;

 typedef mpl::find_if<
    signatures,
    predicate<
            mpl::_1,
            mpl::size_t< 4 >,
            mpl::size_t< 5 >
        >
    >::type iter_0;

That's not to say that it's something obvious and easy to figure out - I'll
look if there is a simple way to workaround the compiler's deficiency that
doesn't have this idiosyncrasy.

Aleksey