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// A simple example of an unsound mixing of cyclic structure and Drop.
//
// Each `D` has a name and an optional reference to another `D`
// sibling, but also implements a drop method that prints out its own
// name as well as the name of its sibling.
//
// By setting up a cyclic structure, the drop code cannot possibly
// work. Therefore this code must be rejected.
//
// (As it turns out, essentially any attempt to install a sibling here
// will be rejected, regardless of whether it forms a cyclic
// structure or not. This is because the use of the same lifetime
// `'a` in `&'a D<'a>` cannot be satisfied when `D<'a>` implements
// `Drop`.)
use std::cell::Cell;
struct D<'a> {
name: String,
p: Cell<Option<&'a D<'a>>>,
}
impl<'a> D<'a> {
fn new(name: String) -> D<'a> { D { name: name, p: Cell::new(None) } }
}
impl<'a> Drop for D<'a> {
fn drop(&mut self) {
println!("dropping {} whose sibling is {:?}",
self.name, self.p.get().map(|d| &d.name));
}
}
fn g() {
let (d1, d2) = (D::new(format!("d1")), D::new(format!("d2")));
d1.p.set(Some(&d2));
//~^ ERROR `d2` does not live long enough
d2.p.set(Some(&d1));
//~^ ERROR `d1` does not live long enough
}
fn main() {
g();
}
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