问题
I have a third party C library exporting lots of preprocessor macros with arguments.
Problem is when I try to access them in Swift it fails with:
Unable to resolve the symbol.
What is the way to access such C macros, exported by third party libraries, in Swift?
I do not want to workaround by directly calling functions with name starting with __ and make my code look ugly nor do want to edit/hack third party library.
回答1:
There is no easy answer. The aforementioned Apple documentation states this pretty clearly:
Complex macros are used in C and Objective-C but have no counterpart in Swift.
But, if you really need to call those (ugly!) C macros, you could define C99 inline functions around them (and call those instead from your Swift code).
For instance, given this C macro:
#define SQUARE(n) n * n
Define this C function in another header file:
inline double square(double n) {
return SQUARE(n);
}
Not the exact same thing I'm aware — note that I had to commit to the double number type; those crazy text/symbol manipulation won't work either; etc — but might get you halfway there :)
Pure Swift alternative. Of course, you could also convert all those C macros to idiomatic Swift functions by hand, using protocols, generics, etc to emulate some of the C macros magic.
If I went this route — being the paranoid engineer that I'm! — I would compare the MD5 of the original, converted header against the current file version and fail the Xcode build if both hashes don't match.
This could easily be done by a pre-action build script such as:
test EXPECTED_HASH != $(md5 HEADER_PATH) && exit 1
If this build step fails, then it's time to review your (manually) converted Swift code and update the EXPECTED_HASH afterwards :)
来源：https://stackoverflow.com/questions/43663917/accessing-c-macros-in-swift