rust/src/test/run-pass/option-unwrap.rs

// Copyright 2012 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.

struct dtor {
    x: @mut int,

}

#[unsafe_destructor]
impl Drop for dtor {
    fn finalize(&self) {
        // abuse access to shared mutable state to write this code
        unsafe {
            *self.x -= 1;
        }
    }
}

fn unwrap<T>(+o: Option<T>) -> T {
    match o {
      Some(v) => v,
      None => fail!()
    }
}

pub fn main() {
    let x = @mut 1;

    {
        let b = Some(dtor { x:x });
        let c = unwrap(b);
    }

    assert!(*x == 0);
}