在Swift中访问C宏 [英] Accessing C macros in Swift
问题描述
我有一个第三方C库，可导出带有参数的预处理器宏。
I have a third party C library exporting lots of preprocessor macros with arguments.
问题是当我尝试在Swift中访问它们时它会失败，并显示以下信息：
Problem is when I try to access them in Swift it fails with:
无法解析该符号。
Unable to resolve the symbol.
通过Swift访问第三方库导出的C宏的方法是什么？
What is the way to access such C macros, exported by third party libraries, in Swift?
我不想通过直接调用以 __ 开头的名称的函数来解决问题，并使我的代码看起来丑陋，也不想编辑/修改第三方库。
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.
推荐答案
没有简单的答案。前述 Apple文档非常清楚地说明了这一点：
There is no easy answer. The aforementioned Apple documentation states this pretty clearly:
复杂的宏用于C和Objective-C，但没有
Complex macros are used in C and Objective-C but have no counterpart in Swift.
但是，如果您确实需要调用这些（丑陋的）C宏，则可以定义C99 inline 周围的函数（然后从您的Swift代码中调用这些函数）。
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).
例如，给定此C宏：
#define SQUARE(n) n * n
在另一个头文件中定义此C函数：
Define this C function in another header file:
inline double square(double n) {
return SQUARE(n);
}
我知道的 exact 并非同一件事—请注意，我必须使用 double 数字类型；那些疯狂的文字/符号操作也不起作用；等等-但可能会让您半途而废：）
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替代。当然，您也可以使用 protocols ， generics 等来模拟其中一些C语言宏，从而将 all 所有C宏手动转换为Swift惯用函数。 C宏魔术。
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.
如果我走这条路，那我就是个偏执狂的工程师！ —我将原始转换后的标头的MD5与当前文件版本进行比较，如果两个哈希都不匹配，则Xcode构建将失败。
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.
这很容易做到通过 pre-action 构建脚本，例如：
This could easily be done by a pre-action build script such as:
test EXPECTED_HASH != $(md5 HEADER_PATH) && exit 1
如果此构建步骤失败，那么现在是时候检查您的（手动）转换后的Swift代码了，然后更新 EXPECTED_HASH ：）
If this build step fails, then it's time to review your (manually) converted Swift code and update the EXPECTED_HASH afterwards :)
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