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

On 6/13/2015 11:32 AM, Rob Stewart wrote:

On June 13, 2015 10:01:33 AM EDT, Edward Diener wrote:

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On 6/13/2015 7:13 AM, Rob Stewart wrote:

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On June 12, 2015 10:26:49 PM EDT, Edward Diener wrote:

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On 6/12/2015 1:05 PM, Peter Dimov wrote:

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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.

Yes, that is how I intended SD-6 should be used in Boost.config. I have explained that numerous times in my replies on this thread.

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.

Of course not but we already deal with buggy support anyway in config. I do not mean to replace config's knowledge now or in the future of buggy support for compiler features with blind trust in whatever SD-6 says or whatever a particular compiler or standard library says. If we empirically know that some feature or standard library implementations is not working we mark it accordingly in config. Nothing whatever changes in config if we use SD-6 where appropriate in this respect.