Re: [boost] [MPL] Type detection

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2003-10-23 02:32:55

David B. Held writes:
> Is it possible to detect whether a template parameter is
> an MPL container or not?  

Yep, please see below.

> I would like to be able to do
> something roughly like this:
>
> template <typename T>
> struct foo
> {
>     typedef if_<is_mpl_container<T>::type,
>         begin<T>::type,
>         T
>     >::type my_type;
> };

template <typename T>
struct foo
{
      typedef if_< is_sequence<T>
        begin<T>::type,
        T
    >::type my_type;
};

>
> Actually, what I would really like to do is create an array
> of objects based on the types in T if T is an MPL container,
> and an array of 1 if it's not.  That way, I can say:
>
> foo<int> f;
>
> or:
>
> foo<mpl::list<int, double, char> > f;

You need this one, then:

    template <typename T>
    struct foo
    {
       typedef typename as_sequence<T>::type seq;
       //               ^^
    };

Aleksey