Eric Niebler wrote:
Some tests of Boost.Phoenix fail on clang trunk in a C++11 mode due to narrowing conversions of non-type template arguments, which are prohibited in C++11.
Really?! Wow, that's a breaking change I hadn't heard of before.
Let me elaborate a bit. On clang-cxx11-r155296 test runner, ( http://www.boost.org/development/tests/trunk/developer/phoenix.html ) there are many failures due to the following errors. boost/proto/matches.hpp:354:17: error: non-type template argument evaluates to 2, which cannot be narrowed to type 'bool' [-Wc++11-narrowing] boost/proto/matches.hpp:363:21: error: non-type template argument evaluates to 2, which cannot be narrowed to type 'bool' [-Wc++11-narrowing] The problem is that remove_reference< typename when<_, If>::template impl<Expr, int, int>::result_type >::type::value evaluates to "2", which is not in the range of bool. This causes the compiler errors.
Ideally, this should be a valid MPL Integral Constant of type bool, like:
template< class T > struct is_placeholder : mpl::false_ {};
If that is not portable enough, it could be:
template< class T > struct is_placeholder { BOOST_STATIC_CONSTANT(bool, value = false); };
Neither of them solve the problem. After applying the proposed change, we still have the same errors. Regards, Michel