Re: [v3 PATCH] Implement D0013R2, logical type traits.

[Jonathan Wakely <jwakely@redhat.com>]

On 12/11/15 00:06 +0200, Ville Voutilainen wrote:
>--- a/gcc/testsuite/g++.dg/cpp0x/Wattributes1.C
>+++ b/gcc/testsuite/g++.dg/cpp0x/Wattributes1.C
>@@ -5,4 +5,4 @@
> #include <new>
> __attribute__((visibility("hidden")))void*operator new(std::size_t); // { dg-warning "visibility attribute ignored" }
>
>-// { dg-message "previous declaration" "" { target *-*-* } 111 }
>+// { dg-message "previous declaration" "" { target *-*-* } 116 }
>diff --git a/libstdc++-v3/include/experimental/type_traits b/libstdc++-v3/include/experimental/type_traits
>index b0ed3b0..b7f3bda 100644
>--- a/libstdc++-v3/include/experimental/type_traits
>+++ b/libstdc++-v3/include/experimental/type_traits
>@@ -271,6 +271,28 @@ template<typename _To, template<typename...> class _Op, typename... _Args>
>   constexpr bool is_detected_convertible_v
>     = is_detected_convertible<_To, _Op, _Args...>::value;
>
>+#if __cplusplus > 201402L
>+
>+#define __cpp_lib_experimental_logical_traits 201511
>+
>+using std::conjunction;
>+using std::disjunction;
>+using std::negation;

It's unfortunate if the std::experimental versions are only available
for C++17 mode, because the whole point of putting it into both C++17
and the TS was that users can make us of the std::experimental
versions sooner than they can make use of C++17 version. If both
versions depend on using -std=c++17 then the TS versions are entirely
redundant.

So I think we want to define them again, independently, in
<experimental/type_traits>, even though it might lead to ambiguities
for code that does:

using namespace std;
using namespace std::experimental;