Re: [boost] Problem with detail/identifier.hpp

From: Beman Dawes (bdawes_at_[hidden])
Date: 2006-11-13 17:24:14

Matthias Troyer wrote:

> Due to recent changes to the filesystem library now, the header  
> detail/identifier.hpp is now included in my projects and contains the  
> dangerous code segment:
> 
>    template <class Ostream, class Id>
>      typename enable_if< is_base_of< identifier< typename  
> Id::value_type, Id >, Id >,
>        Ostream & >::type operator<<( Ostream & os, const Id & id )
>    {
>      return os << id.value();
>    }
> 
> which breaks all of my codes, since I have a type Id, that has a type  
> member Id::value_type which is an abstract base class. My compiler  
> (Apple gcc-4.0) now tries to instantiate identifier< typename  
> Id::value_type, Id >, which fails because Id::value_type is abstract,  
> and the compiler aborts with an error message.
> 
> This causes all of our codes to fail to compile with the current CVS  
> head

There are several things going on here,

* boost/system/error_code.hpp is now included by the filesystem library, 
and also presumably asio. boost/system/error_code.hpp in turn uses 
boost::detail::identifier from boost/detail/identifier.hpp.

* When I moved identifier.hpp into boost/detail, I forgot to also move 
class identifier from namespace boost to namespace boost::detail. That 
has now been corrected in CVS.

* There is a SFINAE issue, as you point out in another post. It works 
with some compilers but not others. I don't have time at the moment to 
sort it out, so simply commented out the insert and extractor for now.

Thanks for the bug report!

--Beman