fn main() {
    let a: Box<dyn Fn(i32)> = Box::new(| x | println!("{:?}", x));

    unsafe {
        use std::slice;
        let ptr = Box::into_raw(Box::new(a));
        let number = ptr as usize;
        let bytes = slice::from_raw_parts(&number as *const _ as *const u8, 8);
        test(bytes);
    };

}

#[no_mangle]
pub unsafe extern "C" fn test(bytes: &[u8]) {
    let number = *(bytes.as_ptr() as *const usize);
    let ptr = number as *mut Box<dyn Fn(i32)>;
    let b = Box::from_raw(ptr);
    b(5);
}