Attribute Macro vtable

#[vtable]

Defines a struct that will act as a VTable to a C++ class. It can also take data as to make sure the class functions as expected.

Example

#define interface class __declspec(novtable)
interface MathEngine {
public:
        virtual int add(int x, int y) = 0;
        virtual int add2(int x, int y) = 0;
};

class MyEngine: public MathEngine {
public:
    int mynum;

    MyEngine(int b) {
        mynum = b;
    }

    virtual int add(int x, int y) {
        return x + y;
    }

    virtual int add2(int x, int y) {
        return mynum + x + y;
    }
};

extern "C" {
    MyEngine* getMath(int b) {
    return new MyEngine(b);
}
};

use std::os::raw::c_int;
use viable_impl::*;
extern "C" {
    fn getMath(b: c_int) -> *mut MathIFace;
}

use viable_impl::vtable;
#[vtable]
struct MathIFace {
    internal: i32,

    #[offset(0)]
    add: fn(a: c_int, b: c_int) -> c_int,
    add2: fn(a: c_int, b: c_int) -> c_int,
}

pub fn main() {
    let iface = unsafe { getMath(10) };
    let iface = unsafe { iface.as_mut().unwrap() };

    let value = iface.add2(5, 5);

   assert_eq!(value, 10 + 5 + 5);
}