4 ms·

That's not really "simple", it's on par with C FFI in about any other language (except C++), with same drawbacks.

• gizmo686 2y ago
  ... And? Most languages make C interop simple.
  • varjag 2y ago
    They quickly become unwieldy on non-trivial APIs, with hundreds of definitions across dozens of files and with macros to boot. Naturally people would still get the job done but it's beyond simple.
    • mcronce 2y ago
      That's what bindgen is for, as was mentioned in the original comment you replied to.
      • varjag 2y ago
        How well does it handle preprocessor macros in APIs?
        • marshray 2y ago
          I have used it successfully against header files for Win32 COM interfaces generated from IDL which include major parts of the infamous "windows.h". Almost every type is a macro. This is an extremely well-understood space. Just open the docs and do it.
          • varjag 2y ago
            Not types, functions. Where the macro is essentially a forward declaration but the implementation is deep inside the code and is not exposed via headers.
• commodoreboxer 2y ago
  It's on par with C++, too. In C++ you need an `extern "C"`, because C++ linkage isn't guaranteed to be the same as C linkage. You can get away with wrapping that around it in a preprocessor conditional, but that's not all that much easier than Rust's bindgen. A lot of C to C++ interop is actually done wrong without knowing it. Throwing a C++ static function as a callback into a C function usually works, but it's not technically correct because the linkage isn't guaranteed to be the same without an extern "C". In practice, it usually is the same, but this is implementation-defined, and C++ could use a different calling convention from C (e.g. cdecl vs fastcall vs stdcall. The Borland C++ compiler uses fastcall by default for C++ functions, which will make them illegal callbacks for C functions). The major difference between Objective-C and C++'s C interop and other languages is the lack of the preprocessor. Macros will just work because they use the same preprocessor. That's really not easy to paper over in other languages that can't speak the C preprocessor.
  • spacechild1 2y ago
    I think you're confusing some terms here. > In C++ you need an `extern "C"`, because C++ linkage isn't guaranteed to be the same as C linkage. `extern "C"` has nothing to do with linkage, all it does is disable namemangling, so you get the same symbol name as with a C compiler. > Throwing a C++ static function as a callback into a C function usually works, but it's not technically correct because the linkage isn't guaranteed to be the same without an extern "C". Again, linkage is not relevant here. Your C++ callbacks don't have to be declared as extern "C" either, because the symbol name doesn't matter. As you noted correctly, the calling conventions must match, but in practice this only matters on x86 Windows. (One notable example is passing callbacks to Win32 API functions, which use `stdcall` by default.) Fortunately, x86_64 and ARM did away with this madness and only have a single calling convention (per platform).
    • LegibleCrimson2 2y ago
      > `extern "C"` has nothing to do with linkage, all it does is disable namemangling, so you get the same symbol name as with a C compiler. extern "C" also ensures that the C calling convention is used, which is relevant for callbacks. It's not just name mangling. This is the reason that extern "C" static functions exist. You can actually overload a C++ function by extern "C" vs extern "C++", and it will dispatch it appropriately based on whether the passed in function is declared with C or C++ linkage. And I'm not sure the terms are confused, because that's how most documentation refers to it: https://learn.microsoft.com/en-us/cpp/cpp/extern-cpp?view=msvc-170#extern-c-and-extern-c-function-declarations https://learn.microsoft.com/en-us/cpp/cpp/extern-cpp?view=ms... > In C++, when used with a string, extern specifies that the linkage conventions of another language are being used for the declarator(s). C functions and data can be accessed only if they're previously declared as having C linkage. However, they must be defined in a separately compiled translation unit. And https://en.cppreference.com/w/cpp/language/language_linkage https://en.cppreference.com/w/cpp/language/language_linkage The post you're replying to had it completely right. extern "C" is entirely about linkage, which includes calling convention and name mangling. > As you noted correctly, the calling conventions must match, but in practice this only matters on x86 Windows. Or if you want your program to actually be correct, instead of just incidentally working for most common cases, including on future systems. If you're passing a callback to a C function from C++, it's wrong unless the callback is declared extern "C".
• kelnos 2y ago
  How is that not simple? You just declare the function and then call it. I find it hard to imagine how it could be any more simple than that.
  • varjag 2y ago
    Now imagine a hundred or two functions, structures and callbacks, some of them exposed only as CPP macros over internal implementation. PJSIP low level API is one example.
    • lambda 2y ago
      But... that's what bindgen is for. Which I mentioned. I said it "can be quite simple"; for simple use cases, just using extern and translating the declarations by hand is perfectly viable. For more complex cases, you use bindgen.
      • varjag 2y ago
        Bindings generators exist in most other languages with same limitations. I would love to see how bindgen would handle a function call defined as a preprocessor macro that I mentioned. Because most likely it won't.
    • googh 2y ago
      Can someone shed some light on why the parent comment (by varjag) is downvoted?