从 C 调用 Swift 的最佳方式是什么? [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 中制作一个双向包装器，所以我的 C 必须调用 Swift 函数.

现在，我可以通过在 C 中声明函数指针，并在 Swift 端设置它们以在 Swift 中调用代码后让我的 C 函数调用它们来实现这一点.

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 void callBackIntoSwift( callback_t cb ){printf( "将回调到 Swift
" );cb();printf( "确实回调到 Swift
" );}

在桥接头中包含我的 C 头文件后，我可以在 Swift 端执行以下操作:

let cb: callback_t = {someKindOfSwiftFunction()}callBackIntoSwift( cb )

甚至:

callBackIntoSwift {someKindOfSwiftFunction()}

在不需要函数指针和回调的情况下，有没有更好的方法来做到这一点?我想让 C 端直接调用 someKindOfSwiftFunction ……但是当我尝试将 @convention (c) 应用于函数声明时，我得到消息，该属性可以仅适用于类型，而不适用于声明.

任何想法或代码库，例如Github我可以看看吗?

解决方案

根据 Joe Groff:

<块引用>

目前还没有正式的方法.除了名称修改之外，Swift 函数使用与 C 不同的调用约定.非正式地，如果您愿意处理比通常数量更多的代码损坏和编译器错误，那么有一个非官方属性 @_cdecl 可以做到这一点:

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

<块引用>

然后你可以从 C: 调用它

#include intptr_t mymodule_foo(intptr_t);intptr_t invoke_foo(intptr_t x) {返回 mymodule_foo(x);}

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.

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.

My C header file:

typedef void (*callback_t)(void);

void callBackIntoSwift( callback_t cb );

My C implementation file:

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

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

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 )

Or even:

callBackIntoSwift {
    someKindOfSwiftFunction()
}

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.

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

解决方案

According to Joe Groff:

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
}

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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