Roles

Package behaviour in roles and compose it into classes with does.

A role is a bundle of methods a class can compose in with does — Raku's answer to "I want to share behaviour without inheritance":

role Greeter {
    method greet() { "Hi, I am { self.name }." }
}

class Robot does Greeter {
    has $.name;
}

class Human does Greeter {
    has $.name;
}

say Robot.new(name => 'R2-D2').greet;
say Human.new(name => 'Ada').greet;

Hi, I am R2-D2.
Hi, I am Ada.

The role calls self.name and trusts whatever class it lands in to provide it.

Composing several roles #

A class can do any number of roles, and roles can carry attributes too:

role CanFly {
    method fly() { "{ self.name } takes off!" }
}
role CanSwim {
    method swim() { "{ self.name } dives in!" }
}

class Duck does CanFly does CanSwim {
    has $.name;
}

my $d = Duck.new(name => 'Donald');
say $d.fly;
say $d.swim;

Donald takes off!
Donald dives in!

Checking for a role #

The .does method asks any object whether it plays a role:

role Loud { }
class Drum does Loud { }
class Flute { }

say Drum.new.does(Loud);
say Flute.new.does(Loud);

True
False

Try it #

Add a Shouter role with a shout method that returns the object's name uppercased, with a ! at the end.

role Shouter {
}

class Coach does Shouter {
    has $.name;
}
say Coach.new(name => 'Bob').shout;

role Shouter {
    method shout() { self.name.uc ~ '!' }
}

class Coach does Shouter {
    has $.name;
}
say Coach.new(name => 'Bob').shout;

BOB!