[Boost-bugs] [Boost C++ Libraries] #3338: proto: const-correctness issue on transforms (array types)

Subject: [Boost-bugs] [Boost C++ Libraries] #3338: proto: const-correctness issue on transforms (array types)
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-08-11 18:41:45

#3338: proto: const-correctness issue on transforms (array types)
-------------------------------------------------------------+--------------
 Reporter:  François Barel <frabar666@…>                     |       Owner:  eric_niebler
     Type:  Bugs                                             |      Status:  new         
Milestone:  Boost 1.40.0                                     |   Component:  proto       
  Version:  Boost Development Trunk                          |    Severity:  Problem     
 Keywords:  transform _value const function returning array  |  
-------------------------------------------------------------+--------------
 This has been extracted from Spirit2 test failures on gcc in C++0x mode
 (e.g. http://tinyurl.com/mmo2ym). When adding this line to Proto's
 matches.cpp test:
 {{{
 Index: matches.cpp
 ===================================================================
 --- matches.cpp (revision 55531)
 +++ matches.cpp (working copy)
 @@ -172,6 +172,8 @@
      assert_matches< terminal<char [N]> >( as_child("hello") );
      assert_matches< terminal<char [N]> >( as_expr("hello") );

 +    assert_not_matches< if_<is_same<_value, int>()> >( lit("hello") );
 +
      assert_matches< terminal<std::string> >( lit(std::string("hello")) );
      assert_matches< terminal<std::string> >(
 as_child(std::string("hello")) );
      assert_matches< terminal<std::string> >(
 as_expr(std::string("hello")) );
 }}}
 the test no longer compiles on gcc-4.3 or later in C++0x mode, although it
 works fine in non-C++0x mode.

 The error is not the {{{is_same}}} check failing, but happens during
 instantiation of {{{proto::_value}}}:
 {{{
 In file included from matches.cpp:16:0:
 boost/proto/transform/arg.hpp:
   In instantiation of '_value::impl<exprns_::expr<tag::terminal,
         argsns_::term<const char (&)[6]>, 0l>, int, int>':
 ...
 boost/proto/transform/arg.hpp:203:13:
   error: function returning an array
 }}}

 [[br]]

 AFAICT the issue is always there, but becomes visible due to
 {{{BOOST_HAS_DECLTYPE}}} (which gets defined in C++0x mode, and modifies
 the result types of several transforms in {{{transform/arg.hpp}}}).
 Considering {{{_value::impl}}} here:
  - It is called with a terminal containing a {{{char const (&)[6]}}},
  - {{{result_type}}} is always {{{result_of::value<Expr>::type}}} -- here
 {{{char*}}}, which seems incorrect (missing {{{const}}}),
  - When {{{BOOST_HAS_DECLTYPE}}} is defined, the return type of
 {{{operator()}}} is {{{result_type}}} so this generates a compilation
 error,
  - When it is not defined, the return type of {{{operator()}}} becomes
 {{{result_of::value<typename impl::expr_param>::type}}} -- here {{{char
 const (&)[6]}}}, so the test compiles.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3338>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.