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crustffiabstract-data-type

C Abstract Data Type in Rust

I have this code in my header file:

typedef struct _game* Game;

Right now to FFI from Rust I'm doing:

extern "C" {
    pub type Game = usize;
}

Is there a safer way to do this than to treat it like a pointer-sized numeric type? Would this work:

pub struct Game(usize);
Solution

  • You usually model abstract C types in Rust using a pointer to an empty enum:

    pub enum _game {}
pub type Game = *mut _game;

    This approach explicitly highlights the fact that you cannot create values of _game yourself - you can only get a pointer to it from somewhere.

    That said, if you're writing a more high-level wrapper for your library, you should wrap this Game into a more high-level Game, like this:

    extern crate your_library_sys;

pub struct Game(your_library_sys::Game);

    Here your_library_sys is a "sys" crate which contains low-level FFI bindings to the library. This is a convention which is described in Cargo docs.