//#![feature(nll)]

use std::marker::PhantomData;
use std::mem::transmute;
use std::os::raw::c_void;

struct Handler<'a> {
    _marker: PhantomData<std::cell::Cell<&'a ()>>,
}

impl<'a> Handler<'a> {
    pub fn on_change<T>(&self, data: &'a T)
    where
        T: 'a,
    {
        unsafe {
            let user_data: *const c_void = transmute(data);
            println!("{:?}", user_data)
        }
    }
}

fn main() {
    let foo = 1; // this line should be valid
    let handler = Handler {
        _marker: PhantomData,
    };

    //let foo = 1; // this line should be illegal
    handler.on_change(&foo);
    handler.on_change(&foo);
}