Re: [boost] Interest in switch generator

From: Joel de Guzman (joel_at_[hidden])
Date: 2007-02-03 02:39:14

Steven Watanabe wrote:
> AMDG
> 
>     Is there any interest in a function template that generates a switch 
> statement?
> 
> struct f {
>     typedef void result_type;
>     void operator()(mpl::int_<0>) const {
>        std::cout << "2" << std::endl;
>     }
>     void operator()(mpl::int_<1>) const {
>        std::cout << "1" << std::endl;
>     }
>     void operator()(mpl::int_<5>) const {
>        std::cout << "0" << std::endl;
>     }
> };
> 
> int main() {
>     typedef mpl::vector<mpl::int_<0>, mpl::int_<1>, mpl::int_<5> > cases;
>     switch<cases>(5, f()); //prints 0
>     try {
>         switch<cases>(3, f());
>     } catch(bad_switch&) {}
> }

I'm interested. I'll need polymorphic return type handling though.
Something like:

struct f
{
     template <typename Case> struct result;

     template <> struct result<mpl::int_<0> >
         : mpl::identity<char> {};

     template <> struct result<mpl::int_<2> >
         : mpl::identity<float> {};

     template <> struct result<mpl::int_<5> >
         : mpl::identity<std::string> {};

     char operator()(mpl::int_<0>) const;
     float operator()(mpl::int_<1>) const;
     std::string operator()(mpl::int_<5>) const;
};

Regards,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net