rust/src/test/run-pass/borrowck-preserve-box-in-arm-not-taken.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.

// exec-env:RUST_POISON_ON_FREE=1

pub fn main() {
    let x: @mut @Option<~int> = @mut @None;
    match x {
      @@Some(ref y) => {
        // here, the refcount of `*x` is bumped so
        // `y` remains valid even if `*x` is modified.
        *x = @None;
      }
      @@None => {
        // here, no bump of the ref count of `*x` is needed, but in
        // fact a bump occurs anyway because of how pattern marching
        // works.
      }
    }
}