15.6 Enum methods

Methods can be attached to an enum type. Thus, instead of defining an independent function that takes an enum as argument (i.e.: my_function(my_enum_value)), we can define a method attached to the enum type. We will call this method directly onto the object: my_enum_value.my_method().

Let us define a Suit enum for representing card suits:

:clear

#[derive(Debug, PartialEq)]
enum Suit {
  Club,
  Diamond,
  Heart,
  Spade,
}

Using the impl statement we declare the is_black() method that returns true for black color cards (i.e.: clubs and spades):

impl Suit {
  fn is_black(&self) -> bool {
    [Suit::Club, Suit::Spade].contains(self)
  }
}

We can call this method on any Suit instance:

for x in [Suit::Diamond, Suit::Club, Suit::Heart, Suit::Spade] {
  if x.is_black() {
    println!("{x:?}");
  }
}

Club

Spade

see solution