Re: [boost] RFC: type erasure

Subject: Re: [boost] RFC: type erasure
From: Vicente Botet (vicente.botet_at_[hidden])
Date: 2011-05-24 02:34:58

Steven Watanabe-4 wrote:
> 
> AMDG
> 
> On 05/23/2011 02:34 PM, Vicente Botet wrote:
>> I would try to study more deeply your design in order to see the
>> advantage
>> it could provide to my library. While developing Boost.Opaque (available
>> on
>> the sandbox
>> https://svn.boost.org/svn/boost/sandbox/opaque/libs/opaque/doc/html/index.html),
>> I was confronted to a similar problem, that is,  how to add in a
>> declarative
>> way, more operations to the underlying class.  I have reached to manage
>> with
>> this using what I have called a meta-mixin. 
>> 
>> A MetaMixin is a meta-function having as nested type a Mixin. The
>> archetype
>> of a MetaMixin is
>> 
>> struct MetaMixinArchetype {
>>     template (*typename Final, typename Base*)
>>     struct type : Base
>>     {
>>         ...
>>     };
>> };
>> 
>> Metamixins are is a similar way to your concepts, passing them in a
>> mpl-sequence.
>> 
>> I will appreciate a lot if you can take a look and comment the design of
>> Boost.Opaque.
>> 
> 
> It looks like your MetaMixin is pretty much
> equivalent to what I did with concept_interface.
> For what you're trying to do, I don't see that it
> can really be improved much.
> 

Thanks for your advice.

> I'd say that for the most part, you're better
> off without the extra complexity in my design.
> I have to generate both the interface and the
> dispatching code from a single specification.
> You only need to define forwarding functions.
> 
> 

Why do you needed to generate the interface and forwarding the call
separately?
Is because you want in addition to be able to emulate concept maps?
Aren't type-erasure and concepts orthogonal?

What I mean is that your library is doing concept-erasure and that trying to
solve just  type-erasure could maybe be simpler.

I'm wondering if type_erasure had a MPL sequence of something like my
meta-mixins, the meta-mixing could always forward the call to a concept
adapter if what we want is concept erasure.

Please note that I don't understand yet the whole design of
Boost.TypeErasure.

Best,
Vicente

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