Re: [boost] [type_erasure] Some issues

Subject: Re: [boost] [type_erasure] Some issues
From: Fabio Fracassi (f.fracassi_at_[hidden])
Date: 2013-02-25 14:30:36

On 2/25/13 6:13 PM, Steven Watanabe wrote:
> AMDG
>

[snip]
>> First I think I discovered a bug either in your lib or in clang(with
>> libc++) when compiling one of the documentation examples in C++11 mode.
>>
>
> I haven't tested much with clang in C++11 mode.
> I wasn't able to get libc++ working on Linux.
> Are you using the latest version: r83101?
> Also, exactly what version of clang are you
> using?  I'll take a look at this later today.
>

Just updated to revision 83153 (boost sandbox), The problem remains.
I am using
Apple LLVM version 4.2 (clang-425.0.24) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.2.0
Thread model: posix
(the one which comes with XCode 4.6)

If you like I can send you the output of running your test suite.

[snip]
>
> The problem is the way name lookup works.  It's clear that
> draw can't be found in the template definition, since it
> isn't declared until later on.  Argument dependent lookup
> usually works, but in this case, the only associated namespace
> is std (from std::ostream) and draw is defined in the global
> namespace. (Note that the built-in types have no associated
> namespaces).  BOOST_TYPE_ERASURE_FREE will have exactly
> the same problem.  The solution is add declarations of draw
> for all builtin types /before/ the definition of drawable.

Ok, this works, but makes it impossible to (reliably) define the concept 
in isolation.
Quite a severe limitation. Is there any possibility to overcome this?

>> On researching a better solution I saw that you already added the
>> convenience macros BOOST_TYPE_ERASURE_MEMBER and
>> BOOST_TYPE_ERASURE_FREE, but didn't have much luck with them.
>> Is there a compileable example where they are used somewhere?
>>
>
> libs/type_erasure/example/basic.cpp uses both.
> See also libs/type_erasure/test/member.cpp
> and libs/type_erasure/test/free.cpp.
>

I see. This seems to be another problem which has to do with the C++11 
mode.

Best regards

Fabio