[swift-users] A problem about interact with C macros

[Geordie Jay]

I think this is because the C preprocessor will interpret SITUATIONALL not
as a value but as an expression. That means your C code at that spot will
be turned into “(SITUATION1 | SITUATION2 | etc)” and not into the result of
that expression directly.

The clang importer could probably figure this out, but I suspect there are
diminishing returns in figuring out what really is a constant as opposed to
another expression etc. Especially in this example, the inconvenience of
defining your own SITUATIONALL in Swift is likely lower than the
inconvenience of that where the macro expression imports incorrectly and
does unexpected things.

Please (anyone) correct me if I’m wrong here though, I’d like to know the
definitive answer myself.

- Geordie

Li Keqing via swift-users <swift-users at swift.org> schrieb am So. 17. Dez.
2017 um 13:08:

> Here are some macros in C headers such as
>
> #define SITUATION1 0x00000001
> #define SITUATION1 0x00000002
> #define SITUATION3 0x00000004
> #define SITUATION4 0x00000008
> #define SITUATIONALL (SITUATION1 | SITUATION2 | SITUATION3 | SITUATION4)
>
> when use these value in swift
> those lines are okay
> let value1 = SITUATION1
> let value2 = SITUATION2
> let value3 = SITUATION3
> let value4 = SITUATION4
> but this line would show error
> let valueAll = SITUATIONALL
>
>  Is it a bug ? or just be designed as it?
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