[Boost-bugs] [Boost C++ Libraries] #7763: Boost.Parameter functions no longer accept non-moveable types as arguments

Subject: [Boost-bugs] [Boost C++ Libraries] #7763: Boost.Parameter functions no longer accept non-moveable types as arguments
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-12-04 04:00:23

#7763: Boost.Parameter functions no longer accept non-moveable types as arguments
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 Reporter:  John Bytheway <jbytheway+boost@…>          |       Owner:  danielw   
     Type:  Bugs                                       |      Status:  new       
Milestone:  To Be Determined                           |   Component:  parameter 
  Version:  Boost 1.52.0                               |    Severity:  Regression
 Keywords:                                             |  
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 Boost.Parameter suffered a regression because of a change to the semantics
 of boost::is_convertible.  It used to be possible to pass a non-movable
 type to a Boost.Parameter function, but that no longer works as of Boost
 1.47 (at least on certain compilers; gcc continued to work for some more
 Boost versions but doesn't in 1.52).

 The issue with is_convertible was discussed in more detail in this thread:
 http://boost.2283326.n4.nabble.com/type-traits-parameter-Inconsistent-

 boost-is-convertible-between-gcc-and-clang-td4634162.html

 It first manifested in clang, but now also appears in gcc thanks to the
 bugfix discussed that thread.

 I attach an example demonstrating the problem.

 I have worked around the problem locally by editing
 boost/parameter/preprocessor.hpp and changing

     typedef is_convertible<mpl::_, Target> type;

 to

     typedef is_convertible<mpl::_, const Target&> type;

 I make no claim that this is exactly the correct fix, but I believe
 something along these lines is required.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7763>
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