Keyboard shortcuts

Press or to navigate between chapters

Press S or / to search in the book

Press ? to show this help

Press Esc to hide this help

box_patterns

The tracking issue for this feature is: #29641


Note: This feature will be superseded by deref_patterns in the future.

Box patterns let you match on Box<T>s:

#![feature(box_patterns)] fn main() { let b = Some(Box::new(5)); match b { Some(box n) if n < 0 => { println!("Box contains negative number {n}"); }, Some(box n) if n >= 0 => { println!("Box contains non-negative number {n}"); }, None => { println!("No box"); }, _ => unreachable!() } }