A basic example of the Strategy pattern implemented in Rose.

TeresaStrategyPatternRose.rose

use std::util::Random
pub abs trait MeleeAttackBehavior begin
    pub abs def meleeAttack(self: &Self) -> Int
end
pub abs trait RangedAttackBehavior begin
    pub abs def rangedAttack(self: &Self) -> Int
end
pub trait Melee3d6 impl MeleeAttackBehavior begin
    pub def meleeAttack(self: &Melee3d6) -> Int do
        let rnd := new Random()
        rnd.nextInt(6)+rnd.nextInt(6)+rnd.nextInt(6)+3
    end
end
pub trait Melee2d4 impl MeleeAttackBehavior begin
    pub def meleeAttack(self: &Melee2d4) -> Int do
        let rnd := new Random()
        rnd.nextInt(4)+rnd.nextInt(4)+2
    end
end
pub trait Ranged2d4 impl RangedAttackBehavior begin
    pub def rangedAttack(self: &Ranged2d4) -> Int do
        let rnd := new Random()
        rnd.nextInt(4)+rnd.nextInt(4)+2
    end
end
pub trait NoRangedAttack impl RangedAttackBehavior begin
    pub def rangedAttack(self: &NoRangedAttack) => 0
end
pub abs class Character begin
    health: Int
    has melee: impl MeleeAttackBehavior
    has ranged: impl RangedAttackBehavior
    pub Character(self: &mut Character, health: Int, melee: impl MeleeAttackBehavior, ranged: impl RangedAttackBehavior) do
        self.health = health
        self.melee = melee
        self.ranged = ranged
    end
    pub def wound(self: &mut Character, dmg: &Int) -> Bool do
        self.health = (self.health > dmg) ? self.health-dmg : 0
        self.health == 0
    end
end
pub class Knight ext Character begin
    pub Knight(self: &mut Knight) => self.super(18, new Melee3d6(), new NoRangedAttack())
end
pub class Rogue ext Character begin
    pub Rogue(self: &mut Rogue) => self.super(12, new Melee3d6(), new Ranged2d4())
end
pub class GiantRat ext Character begin
    pub GiantRat(self: &mut GiantRat) => self.super(10, new Melee2d4(), new NoRangedAttack())
end