src/doc/unstable-book/src/language-features/box-patterns.md

   1 # `box_patterns`
   2
   3 The tracking issue for this feature is: [#29641]
   4
   5 [#29641]: https://github.com/rust-lang/rust/issues/29641
   6
   7 See also [`box_syntax`](box-syntax.md)
   8
   9 ------------------------
  10
  11 Box patterns let you match on `Box<T>`s:
  12
  13
  14 ```rust
  15 #![feature(box_patterns)]
  16
  17 fn main() {
  18     let b = Some(Box::new(5));
  19     match b {
  20         Some(box n) if n < 0 => {
  21             println!("Box contains negative number {}", n);
  22         },
  23         Some(box n) if n >= 0 => {
  24             println!("Box contains non-negative number {}", n);
  25         },
  26         None => {
  27             println!("No box");
  28         },
  29         _ => unreachable!()
  30     }
  31 }
  32 ```