[LLVMdev] C++14 support for shared_mutex

[Edward Diener]

On 6/9/2015 12:15 AM, Stefanus Du Toit wrote:
> On Mon, 8 Jun 2015 at 20:57 Edward Diener
> <eldlistmailingz at tropicsoft.com <mailto:eldlistmailingz at tropicsoft.com>>
> wrote:
>
>     How can I tell at compile time through predefined macros whether libc++
>     includes/supports the C++14 header file shared_mutex ?
>
>
> If you just want to see whether the header exists, and are using Clang
> or GCC 5, you can use __has_include:
>
> http://clang.llvm.org/docs/LanguageExtensions.html#include-file-checking-macros
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__clang.llvm.org_docs_LanguageExtensions.html-23include-2Dfile-2Dchecking-2Dmacros&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=Mfk2qtn1LTDThVkh6-oGglNfMADXfJdty4_bhmuhMHA&m=OBReYKDPkf2rIiHX9dCaocBlBS1aWqjyHfv96KXGjfE&s=yjq9jFWbl69Ob-COO8Wa4Pjq1ERvEIh_s0BHGssfbr0&e=>

Amusingly I see a shared_mutex header file for gcc 4.9. But I would need 
GCC 5 to tell me it exists using the include file checking macros at 
compile time. And which version of clang would I need to use that facility ?

Shouldn't this be a libc++ problem to solve ? After all the potential 
shared_mutex can be or not be part of libc++, and libc++ was designed, 
was it not, to be potentially used by any compiler. So relying on a 
particular compiler to tell me what libc++ should be telling me, seems 
not a good design.

I notice libc++ has a _LIBCPP_VERSION macro. Couldn't libc++ at least 
document somewhere that for any given version _LIBCPP_VERSION it 
supports some given list of libraries ? That would be sensible in my 
mind. Then what it supports is independent of the compiler which uses it.

>
>     Given that I have identified that libc++ is being used, will this
>     work ? :
>
>     #if __cplusplus >= 201402
>     // Header file shared_mutex supported
>     #endif
>
>     or do I need to check something else ?