Re: [boost] Interest in switch generator

From: Steven Watanabe (steven_at_[hidden])
Date: 2007-02-02 21:28:36

Tobias Schwinger <tschwinger <at> isonews2.com> writes:

> 
> Hi Steven,
> 
> Steven Watanabe wrote:
> > AMDG
> > 
> >     Is there any interest in a function template that generates a switch 
> > statement?
> > 
> 
> Yes. I'm interested.
> 
> > 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&) {}
> > }
> > 
> 
> Is this an interface proposal or just some code to illustrate the idea?
> 

Yes this was how the interface would look. I also have
a three parameter version to handle default

> I'd like to have templatized parameters and probably separate function 
> objects for the cases rather than shape-shifting overloads...

I did it this way to allow usage like

template<class FusionSequence>
struct print_nth {
    template<class Index>
    void operator()(Index) const {
        std::cout << fusion::at<Index>(sequence) << std::endl;
    }
    print_nth(const FusionSequence& s) : sequence(s) {}
    const FusionSequence& sequence;
};

> 
> Regards,
> Tobias
>