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use std::ops::Deref;
use std::rc::Rc;
pub struct RcRef<T, U> {
_keep_alive: Rc<T>,
_reference: *const U
}
impl<T, U> RcRef<T, U> {
pub fn new<F>(rc: Rc<T>, f: F) -> RcRef<T, U> where F: FnOnce(&T) -> &U {
RcRef {
_reference: f(&*rc),
_keep_alive: rc,
}
}
pub fn new_opt<F>(rc: Rc<T>, f: F) -> Option<RcRef<T, U>> where F: FnOnce(&T) -> Option<&U> {
f(&*rc).map(|r| r as *const U).map(move |r| RcRef {
_reference: r,
_keep_alive: rc,
})
}
}
impl<T, U> Deref for RcRef<T, U> {
type Target = U;
fn deref(&self) -> &U { unsafe { &*self._reference } }
}
#[test]
fn it_works() {
let a = Rc::new(Some(5));
let b = RcRef::new(a, |opt| opt.as_ref().unwrap());
assert_eq!(*b, 5);
let a = Rc::new(Some(5));
let b = RcRef::new_opt(a, |opt| opt.as_ref()).unwrap();
assert_eq!(*b, 5);
}