pon., 24 mar 2025 o 17:10 Jonathan Wakely <cxx_at_[hidden]> napisał(a):
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> On Mon, 24 Mar 2025 at 16:09, Marcin Jaczewski <marcinjaczewski86_at_[hidden]> wrote:
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>> pon., 24 mar 2025 o 17:07 Jonathan Wakely via Std-Proposals
>> <std-proposals_at_[hidden]> napisał(a):
>> >
>> >
>> >
>> > On Mon, 24 Mar 2025 at 15:56, Matheus Izvekov via Std-Proposals <std-proposals_at_[hidden]> wrote:
>> >>
>> >> I don't disagree in principle with the idea of allowing more kinds of
>> >> attributes, which currently ignorability rules out.
>> >>
>> >> But I think the status quo with vendor attributes is not very safe.
>> >> Either they should be mandatory to implement, or the compiler should
>> >> make it ill-formed
>> >> to use an attribute it doesn't know about, which seems would be quite
>> >> a breaking change.
>> >
>> >
>> > "ill-formed" only requires a diagnostic, which can be a warning. Most compilers already do that for unknown attributes, and have something like -Werror=attributes to make it a hard error.
>> >
>>
>> how then support portable program that use GCC, Clang, MSVC, IC and maybe others
>> that need specific attributes form each compiler?
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> __has_cpp_attribute
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And without `#if`? Macro magic can do a lot but probably a good
solution should stand on its own.
As now we have regions of code that are not parsed at all and could
have syntax errors and typos.
Clean syntax would be prefered that allow external tools to cross
check if all attributes have sens.
Macros can easy confuse them.




>From other email:

>> This is why I would like to have explicit "required" attributes that
>> if older compilers try to parse them fail with invalid syntax exceptions.
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> I was already thinking that [[explicit attr]] could be used instead of your [!!attr]] but it could also be [[requires attr]] (or even [[explicit requires attr]] ... but no).
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Ok `[[explicit foo]]` will work too as now GCC and Clang compliant
that `,` is missing.
Only problem is that `[[explicit(foo)]]` is a valid attribute.
Probaby `[[explicit requires attr]]` would be prefered as most hard to
confuse with normal version.