rust/src/test/run-pass/issue28498-ugeh-ex1.rs

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// Example taken from RFC 1238 text

// https://github.com/rust-lang/rfcs/blob/master/text/1238-nonparametric-dropck.md
//     #example-of-the-unguarded-escape-hatch

#![feature(dropck_parametricity)]
use std::cell::Cell;

struct Concrete<'a>(u32, Cell<Option<&'a Concrete<'a>>>);

struct Foo<T> { data: Vec<T> }

impl<T> Drop for Foo<T> {
    // Below is the UGEH attribute
    #[unsafe_destructor_blind_to_params]
    fn drop(&mut self) { }
}

fn main() {
    let mut foo = Foo {  data: Vec::new() };
    foo.data.push(Concrete(0, Cell::new(None)));
    foo.data.push(Concrete(0, Cell::new(None)));

    foo.data[0].1.set(Some(&foo.data[1]));
    foo.data[1].1.set(Some(&foo.data[0]));
}