Add Strategy (ES5 + ES6 + CoffeeScript + TypeScript)

Author: Badacadabra

doc/GoF/Behavioral/Strategy/README.md

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+# Synopsis
+
+I am playing a fighting game and I do not know my opponent. Should I prefer an offensive or defensive style? 
+
+# Problem
+
+Since the opponent is unknown, the player has to choose a fighting strategy on the fly.
+In programming terms, we can say that an algorithm has to be selected at runtime, among several available algorithms.
+
+# Solution
+
+The Strategy design pattern is exactly what we need in this kind of situation. To implement this pattern, we can have:
+
+  * A concrete context (FightingGame) which contains a reference to a strategy
+  * An abstract representation of a strategy (abstract class or interface)
+  * Concrete strategies (Offense & Defense)

doc/GoF/Behavioral/Strategy/Strategy.dia

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+# ==============================
+# CONCRETE CONTEXT 
+# ==============================
+
+class FightingGame
+    constructor: ->
+        @_strategy = null
+
+    play: ->
+        @_strategy.fight() 
+
+    setStrategy: (fightStyle) ->
+        @_strategy = fightStyle
+
+# ==============================
+# ABSTRACT STRATEGY 
+# ==============================
+
+class Strategy
+    constructor: ->
+        throw new Error "You cannot instantiate an abstract class!" if @constructor is Strategy
+
+    fight: ->
+        throw new Error "You cannot call an abstract method!"
+
+# ==============================
+# CONCRETE STRATEGIES 
+# ==============================
+
+class Offense extends Strategy
+    fight: ->
+        "Fight with an offensive style"
+
+class Defense extends Strategy
+    fight: ->
+        "Fight with a defensive style"
+
+# ==============================
+# CLIENT CODE
+# ==============================
+
+game = new FightingGame
+offense = new Offense
+defense = new Defense
+
+game.setStrategy defense
+console.log "ROUND 1 - #{game.play()}"
+game.setStrategy offense
+console.log "ROUND 2 - #{game.play()}"

doc/GoF/Behavioral/Strategy/Strategy.png

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+// ==============================
+// CONCRETE CONTEXT 
+// ==============================
+
+class FightingGame {
+    private strategy: Strategy;
+
+    play(): string {
+        return this.strategy.fight(); 
+    }
+
+    setStrategy(fightStyle: Strategy): void {
+        this.strategy = fightStyle;
+    }
+}
+
+// ==============================
+// ABSTRACT STRATEGY 
+// ==============================
+
+interface Strategy {
+    fight(): string;
+}
+
+// ==============================
+// CONCRETE STRATEGIES 
+// ==============================
+
+class Offense implements Strategy {
+    fight(): string {
+        return "Fight with an offensive style";
+    }
+}
+
+class Defense implements Strategy {
+    fight(): string {
+        return "Fight with a defensive style";
+    }
+}
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+let game: FightingGame = new FightingGame(),
+    offense: Strategy = new Offense(),
+    defense: Strategy = new Defense();
+
+game.setStrategy(defense);
+console.log(`ROUND 1 - ${game.play()}`);
+game.setStrategy(offense);
+console.log(`ROUND 2 - ${game.play()}`);

src/CoffeeScript/GoF/Behavioral/Strategy/Strategy.coffee

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+'use strict';
+
+// ==============================
+// CONCRETE CONTEXT 
+// ==============================
+
+var FightingGame = (function () {
+    var strategy = null;
+
+    function FightingGame() {}
+
+    FightingGame.prototype.play = function () {
+        return strategy.fight(); 
+    };
+
+    FightingGame.prototype.setStrategy = function (fightStyle) {
+        strategy = fightStyle; 
+    };
+
+    return FightingGame;
+})();
+
+// ==============================
+// ABSTRACT STRATEGY 
+// ==============================
+
+var Strategy = (function() {
+    function Strategy() {
+        if (this.constructor === Strategy) {
+            throw new Error("You cannot instantiate an abstract class!");
+        }
+    }
+
+    Strategy.prototype.fight = function () {
+        throw new Error("You cannot call an abstract method!");
+    };
+
+    return Strategy;
+})();
+
+// ==============================
+// CONCRETE STRATEGIES 
+// ==============================
+
+var Offense = (function () {
+    function Offense() {}
+    Offense.prototype = Object.create(Strategy.prototype);
+    Offense.prototype.constructor = Offense;
+
+    Offense.prototype.fight = function () {
+        return "Fight with an offensive style";
+    };
+
+    return Offense;
+})();
+
+var Defense = (function () {
+    function Defense() {}
+    Defense.prototype = Object.create(Strategy.prototype);
+    Defense.prototype.constructor = Defense;
+
+    Defense.prototype.fight = function () {
+        return "Fight with a defensive style";
+    };
+
+    return Defense;
+})();
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+var game = new FightingGame(),
+    offense = new Offense(),
+    defense = new Defense();
+
+game.setStrategy(defense);
+console.log("ROUND 1 - " + game.play());
+game.setStrategy(offense);
+console.log("ROUND 2 - " + game.play());

src/TypeScript/GoF/Behavioral/Strategy/Strategy.ts

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+// ==============================
+// CONCRETE CONTEXT 
+// ==============================
+
+class FightingGame {
+    constructor() {
+        this._strategy = null;
+    }
+
+    play() {
+        return this._strategy.fight(); 
+    }
+
+    setStrategy(fightStyle) {
+        this._strategy = fightStyle;
+    }
+}
+
+// ==============================
+// ABSTRACT STRATEGY 
+// ==============================
+
+class Strategy {
+    constructor() {
+        if (new.target !== undefined) {
+            throw new Error("You cannot instantiate an abstract class!");
+        }
+    }
+
+    fight() {
+        throw new Error("You cannot call an abstract method!");
+    }
+}
+
+// ==============================
+// CONCRETE STRATEGIES 
+// ==============================
+
+class Offense extends Strategy {
+    fight() {
+        return "Fight with an offensive style";
+    }
+}
+
+class Defense extends Strategy {
+    fight() {
+        return "Fight with a defensive style";
+    }
+}
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+let game = new FightingGame(),
+    offense = new Offense(),
+    defense = new Defense();
+
+game.setStrategy(defense);
+console.log(`ROUND 1 - ${game.play()}`);
+game.setStrategy(offense);
+console.log(`ROUND 2 - ${game.play()}`);