id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
3338	proto: const-correctness issue on transforms (array types)	François Barel <frabar666@…>	Eric Niebler	"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.
"	Bugs	closed	Boost 1.41.0	proto	Boost Development Trunk	Problem	invalid	transform _value _child_c const function returning array