src/test/run-pass/nll/rc-loop.rs

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // A test for something that NLL enables. It sometimes happens that
  12 // the `while let` pattern makes some borrows from a variable (in this
  13 // case, `x`) that you need in order to compute the next value for
  14 // `x`.  The lexical checker makes this very painful. The NLL checker
  15 // does not.
  16
  17 #![feature(match_default_bindings)]
  18 #![feature(nll)]
  19
  20 use std::rc::Rc;
  21
  22 #[derive(Debug, PartialEq, Eq)]
  23 enum Foo {
  24     Base(usize),
  25     Next(Rc<Foo>),
  26 }
  27
  28 fn find_base(mut x: Rc<Foo>) -> Rc<Foo> {
  29     while let Foo::Next(n) = &*x {
  30         x = n.clone();
  31     }
  32     x
  33 }
  34
  35 fn main() {
  36     let chain = Rc::new(Foo::Next(Rc::new(Foo::Base(44))));
  37     let base = find_base(chain);
  38     assert_eq!(&*base, &Foo::Base(44));
  39 }
  40