Re: [boost] Formal Review Request: TypeErasure

Subject: Re: [boost] Formal Review Request: TypeErasure
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2012-06-27 12:21:24

AMDG

On 06/27/2012 08:48 AM, Larry Evans wrote:
> On 06/26/12 14:18, Steven Watanabe wrote:
>> 
>> Anyway, I can compile the following just fine with
>> MSVC 10.
>>
>> int i = 0;
>> call(binding<incrementable<int> >(mpl::map0<>()),
>>     incrementable<int>(), i);
>> // i = 1
> 
> But, AFAICT, that call doesn't have a concept as the 1st arg.
> To make the above call like the ones in my attached file, this
> would have to be:
> 
>   call(incrementable<int>(), i);
> 
> The attached has that, and when it's compiled, it produces errors
> similar to the one previously mentioned here:
> 
> http://article.gmane.org/gmane.comp.lib.boost.devel/232109
> 
> more specifically, the errors include:
> 
> ../../../boost/type_erasure/detail/get_signature.hpp:23:5: error:
> incomplete type 'void' used in nested name specifier
>      BOOST_TYPEOF_NESTED_TYPEDEF_TPL(nested, &Concept::apply)
>      ^
> 
> However, now I realize that's probably because there's no any in
> the argument list, a flaw you mention in the a) problem below.
> So, I'm inferring from your call example, which includes
> the binding<...>(...) arg, that somehow an any arg provides
> something like a binding?
> 
> It would help me if more documentation on the args to
> call were supplied.

I agree.  Here's the requirements in unedited form:

- The binding argument determines the dispatching.
- The concept argument must be present in the binding.
- If a binding is not specified it will be deduced
  from the arguments.  At least one of the arguments
  must be an any.
- Whether an argument is treated as an any is determined
  by the signature of the concept.  Arguments that are
  placeholders are involved in the dispatching.  An
  argument that is an /any/ in the signature of the
  concept gets no special handling.

>  Initially, I had thought call just
> used the 1st arg(the concept) for it's type, and then just
> called that type's static apply with the remaining args
> after, maybe, substituting the placeholders with ...
> Hmm... now I'm not sure what I was thinking, but what's
> becoming clearer to me is I need some more clarification
> on how call works because I'm not having much success
> in using it so far :(
> 

In Christ,
Steven Watanabe