Re: [boost] [config] Using SD-6 macros

Subject: Re: [boost] [config] Using SD-6 macros
From: Edward Diener (eldiener_at_[hidden])
Date: 2015-06-13 10:10:56

On 6/13/2015 5:22 AM, Andrey Semashev wrote:
> On 13.06.2015 05:26, Edward Diener wrote:
>> On 6/12/2015 1:05 PM, Peter Dimov wrote:
>>>
>>> All __cpp_lib macros have an associated header, although I don't know if
>>> we currently have Boost.Config equivalents for any of them.
>>
>> I can see them but they are all C++14 features. Are we really objecting
>> to including a particular standard library header in order to test for
>> the existence of the equivalent SD-6 macro ?
>
> Yes, that would be the objection from my side, at least. I don't want to
> include a whole std header to check for a single feature that may be
> implemented in it. And I want Boost.Config to include most of STL even
> less.

And the rationale for this is what ? Compile-time computer cycles ?

>
>>> It seems to me that there's no macro for SD-6 itself though. When
>>> __cpp_something is not defined, you don't know whether this is because
>>> 'something' is not implemented or because SD-6 is not implemented.
>>
>> What difference could it possibly make ? You test if a macro is defined
>> and if it is not you try something else. If it is you have your answer.
>
> For a compiler that does not support SD-6 you would end up with "the
> compiler does not support C++" with this approach. :) Seriously, you do
> have to know when to check those macros, if you want to know the actual
> capabilities of the compiler.

Of course the SD-6 macro is checked when you need it, not just blindly 
for no reason.

>
> I can see SD-6 only as a helper tool for libraries like Boost.Config and
> not as an alternative. We had various version and feature checks in
> Boost.Config for years, it worked wonderfully and I don't see why it
> would break for the existing compilers we support. Future compilers may
> add features that are currently missing, and we will have to update
> Boost.Config accordingly, whether the compilers use SD-6, misuse it or
> not use it at all.

I am not suggesting replacing Boost.config with SD-6. But as C++ moves 
on in the future SD-6 provides a more fail-safe methodology than the 
wizardry/hackery of current Boost.config.

>
>
> _______________________________________________
> Unsubscribe & other changes:
> http://lists.boost.org/mailman/listinfo.cgi/boost
>