Re: [Boost-bugs] [Boost C++ Libraries] #6974: boost::optional compilation error with boost::function and boost::fusion::vector

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #6974: boost::optional compilation error with boost::function and boost::fusion::vector
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-02-16 00:37:29

#6974: boost::optional compilation error with boost::function and
boost::fusion::vector
------------------------------------------------------------+---------------
  Reporter:  Jonathan Jones <jonathan.jones@…>              |       Owner:  fcacciola
      Type:  Bugs                                           |      Status:  new      
 Milestone:  To Be Determined                               |   Component:  optional 
   Version:  Boost 1.49.0                                   |    Severity:  Problem  
Resolution:                                                 |    Keywords:           
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Comment (by steven_watanabe):

 I'm not quite sure where the best place to fix this is.

 - is_convertible should never fail, but it's probably not feasible to fix
 it.
 - fusion::vector1 shouldn't cause overload resolution to fail, but I don't
 see any way to avoid this problem, given the limitations of
 is_convertible.
 - I could create a special case for is_convertible for boost::function,
 but it would be wrong in some edge cases that a compiler intrinsic (or
 perhaps a C++11 implementation) would be able to get right.
 - That leaves making the copy constructor of optional_base public.  This
 ignores the underlying problem that external code is making assumptions
 about what it can do with an arbitrary type.  I really hate to hack the
 code like this when it isn't the source of the problem.
 - And of course the final option is to modify the constructors so that
 optional_base is never passed to a function that requires overload
 resolution against T.  This one is out because it's too messy.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6974#comment:3>
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