[LLVMdev] C++14 support for shared_mutex

[Edward Diener]

On 6/8/2015 10:10 PM, Tim Northover wrote:
> On 8 June 2015 at 17:53, Edward Diener <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 ?
>
> I doubt it's even theoretically possible. Clang can be used with
> multiple standard libraries, and there's no real way for it to know
> just what you're compiling against (even if it knows in general terms
> that it's libc++).

I am not talking about clang, I am talking about libc++. Is this the 
correct mailing list to ask a question about libc++ or is there a better 
one ? I did not see a separate llvm mailing list for libc++.

>
> On a tightly controlled platform like OS X you might find a mostly
> reliable proxy like the clang version (though people trying to use an
> updated libc++ may curse you for it).

I can tell "in general terms that it's libc++". The Boost.config headers 
can know that from the macro _LIBCPP_VERSION. Once I can tell, you are 
saying that there is no reliable way to tell whether libc++ supports 
shared_mutex, which is currently a completely valid C++14 header file 
and implementation ? That seems pretty poor of libc++. I don't mean to 
be critical but I think that a good standard library creates predefined 
values so that what can tell what is being offered in that library for 
any given release. You can't wait until run-time to include a header 
which may not be there.

I don't want to check anything in clang because, as I understand it, 
libc++ can be and is being used by compilers other than clang. So I 
would assume that either _LIBCPP_VERSION or some other macro connected 
with libc++ should tell me at compile time if shared_mutex is supported.