[boost] Re: Proposal: rational numbers class

From: Moore, Paul (Paul.Moore_at_[hidden])
Date: 1999-12-06 08:16:49

From: Kevlin Henney [mailto:Kevlin.Henney_at_[hidden]]
> In the absence of explicit UDC operators, the suggestion here is to
> introduce a rational_cast template. It has a default implementation
> (following the existing as_* implementations) and can be further
> specialised as necessary:

Yes, I like it. At one stage I had a member template as<type> which did the
same sort of thing - but I like your name better.

One annoyance (and the reason I ditched the as<> approach) is that MS Visual
C++ doesn't like the construct much. (OK, so nobody is surprised - but sadly
I use MSVC). The issue is that

    using boost::rational_cast;
    cout << rational_cast<float>(r);

complains about

rational_test.cpp(25) : error C2679: binary '<<' : no operator defined which
takes a right-hand operand of type '' (or there is no acceptable conversion)
rational_test.cpp(25) : error C2062: type 'float' unexpected

whereas

    cout << boost::rational_cast<float>(r);

works fine.

Does anyone know any magic incantations which would persuade MSVC to accept
this (excluding the obvious one of "go to another compiler vendor")?

Thanks,
Paul.