Re: [Boost-users] [mpl] Inheriting from each type in a sequence

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2007-03-28 04:13:19

Scott Meyers wrote:
> Given some base class,
> 
>    class Base { virtual ~Base(){} };
> 
> I want to be able to implement this:
> 
>    template<typename Seq>
>    const Base& createObject()
>    {
>      // return an object that inherits from Base and every type in Seq
>    }
> 
> The problem is how to create the type of object I want.
> 
> mpl::inherit is almost what I need, but it takes as template parameters each 
> type to inherit from, and I don't have discrete types, I have a sequence of 
> types.  mpl::inherit_linearly takes a sequence and would work for my purposes 
> (which is to create an object that I can later check via dynamic_cast to see if 
> it inherits from a given type), but it works only with forward sequences, and 
> I'll typically have an mpl::set.  I could copy the contents of Seq into an 
> mpl::vector and go from there, but that seems kind of gross.
> 
> Is there a good way to solve this problem that I am overlooking?

An Associative Sequence is a Forward Sequence, so 'inherit_linearly< 
a_set, inherit<_1,_2> >::type' works.

Regards,
Tobias