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

Subject: Re: [boost] [config] Using SD-6 macros
From: Rob Stewart (rob.stewart_at_[hidden])
Date: 2015-06-13 11:32:04

On June 13, 2015 10:01:33 AM EDT, Edward Diener <eldiener_at_[hidden]> wrote:
> On 6/13/2015 7:13 AM, Rob Stewart wrote:
> > On June 12, 2015 10:26:49 PM EDT, Edward Diener
> <eldiener_at_[hidden]> wrote:
> >> On 6/12/2015 1:05 PM, Peter Dimov wrote:
> >>> Edward Diener wrote:
> >>>
> >>> 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.
> >
> > If the absence of an SD-6 macro implies a feature is not
> implemented, then the absence of SD-6 support indicates nothing is
> implemented when that's the mechanism used for discovery of features.
> 
> But who cares ? Each SD=6 feature test stands on its own. I could care
> less if a determination is made "somehow" that SD-6 as a whole is not 
> implemented. It doesn't buy me anything.

You're missing the point. If you can't determine whether SD-6 is available, then you can't just check for the presence of an SD-6 macro to decide whether a feature is available. If the macro isn't present, but SD-6 is supported, then the feature isn't available. If SD-6 isn't supported, then you don't know the answer.

Maybe you mean to try an SD-6 macro to see that a feature is implemented and, if that fails, try other methods before giving up and declaring the feature missing. I suppose that a positive answer from an SD-6 macro could be more reliable, but that doesn't account for buggy support that Boost can't use.

___
Rob

(Sent from my portable computation engine)