Re: [boost] [type_erasure] Review started (July 18-27, 2012)

Subject: Re: [boost] [type_erasure] Review started (July 18-27, 2012)
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2012-07-24 17:39:20

AMDG

On 07/24/2012 10:39 AM, Christophe Henry wrote:
> <snip>
> 
> I find this an interesting question. I use the review to change a
> private but real project and replace all of my OO-style interfaces by
> TypeErasure. I got the following to compile and work (you need
> copy_constructible):
> 
> typedef any< boost::mpl::vector<
>          boost::type_erasure::typeid_<>,
>          boost::type_erasure::copy_constructible<>,
>          boost::type_erasure::addable<>,
>          boost::type_erasure::incrementable<>,
>          boost::type_erasure::decrementable<> >
>                > AnyA;
> 
>        typedef any< boost::mpl::vector<
>          boost::type_erasure::copy_constructible<>,
>          boost::type_erasure::typeid_<>,
>          boost::type_erasure::addable<>
>          >
>        > AnyB;
> 
>          AnyA a(10);
>         AnyB b = a;
> 
> OTOH, this does not compile:
>       AnyB b2(10);
>      AnyA a2=b2;
> 

Right.

> Which brings me to the following use case. Supposing I have 3 classes IA
> <- IB <- IC and 1 object of each held as shared_ptr, I can
> dynamic_pointer_cast from one to another. But if I have 3 any's of
> concepts A,B,C, B containing A's concepts + some more, and C containing
> B's concepts + some more, I can "upcast" as shown above from C to B and
> B to A, but not the other way around, right? Even if I have an object
> fulfilling A,B and C.
> 

That's correct.  As I replied to Fabio in
another thread, this can be implemented,
but requires some kind of reflection.
If enough people need it, I can make
it a priority.

> 
> PS: so far I got only one warning: check_match does not use its
> parameter op.
> 

Fixed.

In Christ,
Steven Watanabe