Pattern Matching

The match keyword let you match a value against one or more patterns. The comparisons are done from top to bottom and the first match wins.

The patterns can be simple values, similarly to switch in C and C++:

fn main() {
    let input = 'x';

    match input {
        'q'                   => println!("Quitting"),
        'a' | 's' | 'w' | 'd' => println!("Moving around"),
        '0'..='9'             => println!("Number input"),
        _                     => println!("Something else"),

The _ pattern is a wildcard pattern which matches any value.

Key Points:

  • You might point out how some specific characters are being used when in a pattern
    • | as an or
    • .. can expand as much as it needs to be
    • 1..=5 represents an inclusive range
    • _ is a wild card
  • It can be useful to show how binding works, by for instance replacing a wildcard character with a variable, or removing the quotes around q.
  • You can demonstrate matching on a reference.
  • This might be a good time to bring up the concept of irrefutable patterns, as the term can show up in error messages.