从C调用Swift的最佳方法是什么？ [英] What is the best way to call into Swift from C?

问题描述

从Swift调用C非常简单，但是我正在考虑在C中创建双向包装，因此我的C必须调用Swift函数。

Calling into C from Swift is pretty simple, however I'm looking into making a bi-directional wrapper in C, so my C has to call Swift functions.

现在，我可以通过在C中声明函数指针，并在Swift端将它们设置为在Swift中调用代码后调用我的C函数来实现。

Right now, I can do this by declaring function pointers in C, and having my C functions call them after the Swift side has set them up to call code in Swift.

我的C头文件：

typedef void (*callback_t)(void);

void callBackIntoSwift( callback_t cb );

我的C实现文件：

#include "stuff.h"
#include <stdio.h>

void callBackIntoSwift( callback_t cb )
{
    printf( "Will call back into Swift\n" );
    cb();
    printf( "Did call back into Swift\n" );
}

在桥接头中包含C头文件后，可以执行以下操作在Swift端：

After including my C header file in the bridging header, I can do the following on the Swift side:

let cb: callback_t = {
    someKindOfSwiftFunction()
}

callBackIntoSwift( cb )

甚至：

callBackIntoSwift {
    someKindOfSwiftFunction()
}

是否有更好的方法来执行此操作，而不需要函数指针和回调？我想让C端直接调用 someKindOfSwiftFunction ……但是当我尝试应用 @convention（c）对于函数声明，我得到的消息是该属性只能应用于类型，而不能应用于声明。

Is there a better way to do this, where function pointers and callbacks are not needed? I'd like to let the C-side call someKindOfSwiftFunction directly … but when I try to apply @convention (c) to function declarations I get the message that the attribute can only be applied to types, and not declarations.

例如，任何想法或代码库Github我可以看看吗？

Any ideas or codebases in e.g. Github I can take a look at?

推荐答案

根据乔·格罗夫（Joe Groff）：

目前尚无官方方法。除了名称修饰之外，Swift函数还使用了与C不同的调用约定。非官方地，如果您愿意处理比平常更多的代码破坏和编译器错误，那么有一个非官方的属性@_cdecl可以做到这一点：

There’s no official way yet. Aside from name mangling, Swift functions use a different calling convention from C. Unofficially, if you’re willing to deal with more than the usual amount of code breakage and compiler bugs, there’s an unofficial attribute @_cdecl that does this:

@_cdecl("mymodule_foo")
func foo(x: Int) -> Int {
  return x * 2
}

然后您可以从C调用它：

which you can then call from C:

#include <stdint.h>

intptr_t mymodule_foo(intptr_t);

intptr_t invoke_foo(intptr_t x) {
  return mymodule_foo(x);
}

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