match

Example from the book (with some more code so it actually does something)

enum Coin {
  Penny,
  Nickel,
  Dime,
  Quarter,
}

fn value_in_cents(coin: Coin) -> u8 {
  match coin {
    Coin::Penny => 1,
    Coin::Nickel => 5,
    Coin::Dime => 10,
    Coin::Quarter => 25,
  }
}

fn main() {

  let my_coin = Coin::Nickel;

  println!("I have {} cents", value_in_cents(my_coin));

}

Make a note that you can put {} for the code blocks, but it's usually not done if it fits on one line.

This is a basic way to use match to do something based off the type of enum that got created.

enum Widget {
  Alfa,
  Bravo
}

fn display_variant(value: Widget) {
  match value {

    Widget::Alfa => {
      println!("kind is Widget::Alfa");
    },

    Widget::Bravo => {
      println!("kind is Widget::Bravo");
    }

  }
}


fn main() {

  let thing1 = Widget::Alfa;
  display_variant(thing1);

  let thing2 = Widget::Bravo;
  display_variant(thing2);

}

Here's anothe example where you pull values out and bind them so you can use them. This is one way to get data out of an enum. (I think if let is another way. Not sure if there are other ways.)

enum Widget {
  Alfa,
  Bravo(String),
  Charlie { value: i32 },
}

fn show_report(item: Widget) {
  match item {
    Widget::Alfa => {
      println!("It's Alfa");
    },
    Widget::Bravo(text) => {
      println!("It's Bravo with {}", text);
    },
    Widget::Charlie { value } => {
      println!("It's Charlie with {}", value);
    },
  }
}

fn main() {
  let item1 = Widget::Alfa;
  show_report(item1);

  let item2 = Widget::Bravo(String::from("hello"));
  show_report(item2);

  let item3 = Widget::Charlie { value: 7 };
  show_report(item3);

}