r##"#[no_mangle]
pub extern "C" fn Test_f(a0: *const C_MyObserver) -> () {
    assert!(!a0.is_null());
    let a0: &C_MyObserver = unsafe { a0.as_ref().unwrap() };
    let a0: Box<dyn OnEvent + Send> = Box::new(a0.clone());
    let mut ret: () = f(a0);
    ret
}"##;

r#"impl OnEvent for C_MyObserver {
    #[allow(unused_mut)]
    fn something_change(&self, a0: i32, a1: &str) -> () {
        let mut a1: CRustStrView = CRustStrView::from_str(a1);
        let ret: () = (self.onStateChanged)(a0, a1, self.opaque);
        ret
    }
}"#;