Re: [Development] (was: Re: C++20 @ Qt)

[Giuseppe D'Angelo via Development]

Il 10/11/22 09:25, Marc Mutz via Development ha scritto:

unconditionally and we will detect post-C++17 library features only this
way, going forward:

    #ifdef __cpp_lib_foo
    # include <foo>
    #endif

and no longer this way:

    #if __has_include(<foo>) && __cplusplus > 201703L
    #  include <foo>
    #endif

To not break existing uses, however, existing checks that do the
__has_include dance should not be cleaned up before we require the resp.
library feature unconditionally.

Hi,



#if __cpp_some_cpp23_feature
# include <cpp23_feature>
#endif



Thanks,

--
Giuseppe D'Angelo | giuseppe.dang...@kdab.com | Senior Software Engineer
KDAB (France) S.A.S., a KDAB Group company
Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
KDAB - The Qt, C++ and OpenGL Experts

I'm not sure if this has been explicitly discussed, but a prerequisite for this scheme to work is that compiler vendors *do not* define library feature macros inside <version> that you cannot use in the current C++ version. In other words, having the proposed: is never going to blow up with some #error inside the included header when compiling in pre-C++23 mode. I'm guessing that's always the case, right?

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