drop_example.rs

// Based on example from: https://doc.rust-lang.org/book/drop.html

struct HasDrop<'a> {
    id: isize,
    next: Option<&'a mut HasDrop<'a>>
}

// Implementing the |Drop| trait causes the errors shown below.
impl<'a> Drop for HasDrop<'a> {
    fn drop(&mut self) {
        println!("Dropping id={}!", self.id);
    }
}

fn drop_mut_borrow<'a>(x: &'a mut HasDrop<'a>) {
    let y = HasDrop { id: 1, next: Some(x) };
}

fn main() {
    let mut x = HasDrop { id: 0, next: None };

    drop_mut_borrow(&mut x);
}

// === Output from |rustc drop_example.rs|:
//
// drop_example.rs:22:26: 22:27 error: `x` does not live long enough
// drop_example.rs:22     drop_mut_borrow(&mut x);
//                                             ^
// drop_example.rs:19:11: 23:2 note: reference must be valid for the block at 19:10...
// drop_example.rs:19 fn main() {
// drop_example.rs:20     let mut x = HasDrop { id: 0, next: None };
// drop_example.rs:21
// drop_example.rs:22     drop_mut_borrow(&mut x);
// drop_example.rs:23 }
// drop_example.rs:20:47: 23:2 note: ...but borrowed value is only valid for the block suffix following statement 0 at 20:46
// drop_example.rs:20     let mut x = HasDrop { id: 0, next: None };
//
// drop_example.rs:21
// drop_example.rs:22     drop_mut_borrow(&mut x);
// drop_example.rs:23 }
// error: aborting due to previous error