Re: [boost] [type_erasure]any(const binding<Concept>&, ...) compile error

Subject: Re: [boost] [type_erasure]any(const binding<Concept>&, ...) compile error
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2012-07-27 15:27:10

AMDG

On 07/27/2012 11:54 AM, Larry Evans wrote:
> On 07/27/12 13:08, Steven Watanabe wrote:
>> 
>> You're passing an argument of type ph_value<_a>.
>> How would constructible<_a(const _a&)> (which
>> is the copy constructor) be viable?
>>
> 
> Because, when _a in constructible<_a(const _a&)> is replaced by the
> binding, it becomes, IIUC,
> 
>   constructible<ph_value<_a>(const  ph_value<_a>&)>
> 

This substitution happens in the dispatching layer.
In the interface of any, constructible<_a(const _a&)>
defines the constructor:

any<C, _a>::any(any<C, const _a&>);

It can't possibly define
any<C, _a>::any(const ph_value<_a>&);
because it doesn't know about ph_value<_a>.

> and this is the same as the compiling version of binding_of.cpp.
> I thought this replacement is what would happen based on the example:
> 
>   constructible<_a(const _b&, const _c&)>
> 
> from:
> 
> 
> http://steven_watanabe.users.sourceforge.net/type_erasure/libs/type_erasure/doc/html/boost_typeerasure/construction.html
> 
> Why is the replacement done in the construction.html example and not
> in bindings_of.cpp?  Hmmm... Ok, the example has any args, from which
> the bindings<ConceptA> can be gotten.  But those same bindings are
> available from the binding<ConceptA> arg in bindings_of.cpp creation
> of a_dup.
> 
> Obviously I'm still missing something, but I've no clue what :(
> 

The library deals with either any's or
with the contained types, but not both,
depending on what layer you're looking at.
You're trying to mix the two.

In Christ,
Steven Watanabe