Re: [boost] BOOST_STATIC_CONSTANT

On 2017-08-17 10:19, Gavin Lambert via Boost wrote:

On 17/08/2017 11:22, Vladimir Batov wrote:

...

There is something seemingly basic that puzzles me greatly. I am hoping people might clarify something I totally fail to understand.

I've been using BOOST_STATIC_CONSTANT for ages (with GCC). Now I have something seemingly non-controversial:

template<typename user_type> struct impl_ptr { using yes_type = boost::type_traits::yes_type; using no_type = boost::type_traits::no_type; using ptr_type = typename std::remove_const::type*;

template<typename Y> static yes_type test (Y*, typename Y::impl_ptr_type* =nullptr); static no_type test (...);

BOOST_STATIC_CONSTANT(bool, value = (1 == sizeof(test(ptr_type(nullptr))))); };

When compiled with gcc-.5.4.0, both lines below pass:

BOOST_TEST(true == boost::impl_ptr<Shared>::value); BOOST_TEST(true == boost::impl_ptr<Shared const>::value);

The only difference between them is "const". However, when I compile with clang-4.0, the second (const) line passes. However, the first one fails! I refuse to believe it's a clang glitch. It must be me doing something really stupid. Help?!

I can't answer this specific question, but since you're targeting C++11 anyway, shouldn't you be using std:: type traits?

So, something like:

template <typename T> class has_impl_ptr_type { template <typename T1> static typename T1::impl_ptr_type test(int); template <typename> static void test(...); public: enum { value = !std::is_void::value }; };

Thanks, Gavin. Is it how it is done these days? Nice. Incorporated. Many thanks... clang still fails... now I am starting to look suspiciously in clang's direction.