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

Subject: Re: [boost] [type_erasure]any(const binding<Concept>&, ...) compile error
From: Larry Evans (cppljevans_at_[hidden])
Date: 2012-07-27 12:49:57

On 07/26/12 11:21, Larry Evans wrote:
> On 07/26/12 09:57, Steven Watanabe wrote:
>> AMDG
>>
>> On 07/26/2012 07:40 AM, Larry Evans wrote:
>>> On 07/26/12 09:02, Steven Watanabe wrote:
>>>> On 07/26/2012 05:29 AM, Larry Evans wrote:
>>>>
>>>> The concept doesn't contain anything that
>>>> matches an argument of type value<_a>.
>>>>
>>> Then why isn't a similar compile error produced when b_any is
> constructed?
>>>
>>
>> This calls a different constructor which
>> has different requirements.  Have you
>> read the reference for any?  I tried
>> to cover the constructors thoroughly.
> 
> My mistake.  I didn't notice:
> 
> 
> http://steven_watanabe.users.sourceforge.net/type_erasure/libs/type_erasure/doc/html/boost/type_erasure/any.html#id2445089-bb
> 
> had:
> 
>   Concept must contain a matching instance of constructible.
> 

The attached, when compiled with:

      #define CONSTRUCTIBLE_PH

fails compilation despite satisfying this Concept constraint
mentioned above.

However, when:

     //#define CONSTRUCTIBLE_PH

it compiles & runs OK.  The compiling version just doesn't use a
placeholder in the args to Sig of constructible.

Why doesn't the one with the placeholder in the Sig args compile?
Maybe I'm not understanding what's meant by:

  Concept must contain a matching instance of constructible.

Could you please explain what I'm missing?

-regards,
Larry