[boost] Re: Re: Policy or Trait?

From: Andy Little (andy_at_[hidden])
Date: 2004-04-03 05:00:18

"Rozental, Gennadiy" <gennadiy.rozental_at_[hidden]> wrote
[example snipped]

> And give me single example where second design is preferable to first?

I agree absolutely. And with the input from contributions this thread under
my belt I shall revisit numeric::converter. There are a large number of
params there .. I guess you think too many?

> Actually I think the best design would look like this:

[example snipped]

Yes this is potentially cool. Unfortunately closest I could get was:

    struct multiply_t
    {
        template< typename A , typename B >
        struct sig : multiply_traits<A,B> {};

        // fails because A and B cannot be deduced from  a or b in the
//function parameters(VC7.1, gcc 3.2)
#if 0
        template< typename A , typename B >
        typename sig<A,B>::result_type
        operator ()( typename sig<A,B>::first_argument_type a,
                            typename sig<A,B>::second_argument_type b )
        {
            return a * b;
        }
#else
        // ok
        template< typename A , typename B >
        typename sig<A,B>::result_type
        operator ()( A const& a,B  b ) //whatever
        {
            return a * b;
        }
#endif

    }multiply;

The unnammed namespace scheme I should think more about ... but off-topic.

regards
Andy Little