Add State (ES5 + ES6 + CoffeeScript + TypeScript)

Author: Badacadabra

doc/GoF/Behavioral/State/README.md

@@ -0,0 +1,17 @@
+# Synopsis
+
+On any computer, I can see a power button. Generally, when the button is pressed while the computer is off, the computer is turned on. And when the button is pressed while the computer is on, the computer is turned off.
+
+# Problem
+
+A computer has two basic states: on and off. So when you press the power button, the system must be smart enough to understand when the computer is on and when it is off. It should also be smart enough to change its own state when the button is pressed.
+
+# Solution
+
+The State design pattern is obviously what we should use here. Here we need: 
+
+  * An abstract representation of a computer state (abstract class or interface)
+  * A concrete computer which is actually the context
+  * Concrete states (on/off)
+
+Contrary to the Strategy pattern, we can access the context directly from the concrete states. This allows state changes from states themselves.

doc/GoF/Behavioral/State/State.dia

@@ -0,0 +1,59 @@
+# ==============================
+# ABSTRACT STATE
+# ==============================
+
+class ComputerState
+    constructor: ->
+        throw new Error "You cannot instantiate an abstract class!" if @constructor is ComputerState
+
+    power: (pc) -> 
+        throw new Error "You cannot call an abstract method!"
+
+# ==============================
+# CONCRETE STATES 
+# ==============================
+
+class Off extends ComputerState
+    power: (pc) -> 
+        pc.setCurrentState pc.getStates().on
+
+class On extends ComputerState
+    power: (pc) -> 
+        pc.setCurrentState pc.getStates().off
+
+# ==============================
+# CONCRETE CONTEXT
+# ==============================
+
+class Computer
+    constructor: ->
+        @_currentState = null
+        @_states =
+            off: new Off
+            on: new On
+
+    power: ->
+        @_currentState.power(@) 
+
+    getCurrentState: ->
+        @_currentState
+
+    setCurrentState: (state) ->
+        @_currentState = state
+
+    getStates: ->
+        @_states
+
+# ==============================
+# CLIENT CODE
+# ==============================
+
+pc = new Computer
+
+pc.setCurrentState pc.getStates().off
+
+console.log pc.getCurrentState().constructor.name # Off
+pc.power()
+console.log pc.getCurrentState().constructor.name # On
+pc.power()
+console.log pc.getCurrentState().constructor.name # Off

doc/GoF/Behavioral/State/State.png

@@ -0,0 +1,70 @@
+// ==============================
+// ABSTRACT STATE
+// ==============================
+
+interface ComputerState {
+    power(pc: Computer): void;
+}
+
+// ==============================
+// CONCRETE STATES 
+// ==============================
+
+class Off implements ComputerState {
+    public power(pc: Computer): void {
+        pc.setCurrentState(pc.getStates().on);
+    }
+}
+
+class On implements ComputerState {
+    public power(pc: Computer): void {
+        pc.setCurrentState(pc.getStates().off);
+    }
+}
+
+// ==============================
+// CONCRETE CONTEXT
+// ==============================
+
+class Computer {
+    private currentState: ComputerState;
+    private states: {off: Off; on: On} = {
+        off: new Off(),
+        on: new On()
+    };
+
+    public power(): void {
+        this.currentState.power(this); 
+    }
+
+    public getCurrentState(): ComputerState {
+        return this.currentState; 
+    }
+
+    public setCurrentState(state: ComputerState): void {
+        this.currentState = state; 
+    }
+
+    public getStates(): {off: Off; on: On} {
+        return this.states; 
+    }
+}
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+let pc: Computer = new Computer();
+
+pc.setCurrentState(pc.getStates().off);
+
+// We extend this TypeScript interface to be able to get class names...
+interface Function {
+    name: string;
+}
+
+console.log(pc.getCurrentState().constructor.name); // Off
+pc.power();
+console.log(pc.getCurrentState().constructor.name); // On
+pc.power();
+console.log(pc.getCurrentState().constructor.name); // Off

src/CoffeeScript/GoF/Behavioral/State/State.coffee

@@ -0,0 +1,93 @@
+'use strict';
+
+// ==============================
+// ABSTRACT STATE
+// ==============================
+
+var ComputerState = (function () {
+    function ComputerState() {
+        if (this.constructor === ComputerState) {
+            throw new Error("You cannot instantiate an abstract class!");
+        }
+    }
+
+    ComputerState.prototype.power = function (pc) {
+        throw new Error("You cannot call an abstract method!");
+    };
+
+    return ComputerState;
+})();
+
+// ==============================
+// CONCRETE STATES 
+// ==============================
+
+var Off = (function () {
+    function Off() {}
+    Off.prototype = Object.create(ComputerState.prototype);
+    Off.prototype.constructor = Off;
+
+    Off.prototype.power = function (pc) {
+        pc.setCurrentState(pc.getStates().on);
+    };
+
+    return Off;
+})();
+
+var On = (function () {
+    function On() {}
+    On.prototype = Object.create(ComputerState.prototype);
+    On.prototype.constructor = On;
+
+    On.prototype.power = function (pc) {
+        pc.setCurrentState(pc.getStates().off);
+    };
+
+    return On;
+})();
+
+// ==============================
+// CONCRETE CONTEXT
+// ==============================
+
+var Computer = (function() {
+    var currentState = null,
+        states = {
+            off: new Off(),
+            on: new On()
+        };
+
+    function Computer() {}
+
+    Computer.prototype.power = function () {
+        currentState.power(this); 
+    };
+
+    Computer.prototype.getCurrentState = function () {
+        return currentState; 
+    };
+
+    Computer.prototype.setCurrentState = function (state) {
+        currentState = state; 
+    };
+
+    Computer.prototype.getStates = function () {
+        return states; 
+    };
+
+    return Computer;
+})();
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+var pc = new Computer();
+
+pc.setCurrentState(pc.getStates().off);
+
+console.log(pc.getCurrentState().constructor.name); // Off
+pc.power();
+console.log(pc.getCurrentState().constructor.name); // On
+pc.power();
+console.log(pc.getCurrentState().constructor.name); // Off

src/TypeScript/GoF/Behavioral/State/State.ts

@@ -0,0 +1,75 @@
+// ==============================
+// ABSTRACT STATE
+// ==============================
+
+class ComputerState {
+    constructor() {
+        if (new.target !== undefined) {
+            throw new Error("You cannot instantiate an abstract class!");
+        }
+    }
+
+    power(pc) {
+        throw new Error("You cannot call an abstract method!");
+    }
+}
+
+// ==============================
+// CONCRETE STATES 
+// ==============================
+
+class Off extends ComputerState {
+    power(pc) {
+        pc.setCurrentState(pc.getStates().on);
+    }
+}
+
+class On extends ComputerState {
+    power(pc) {
+        pc.setCurrentState(pc.getStates().off);
+    }
+}
+
+// ==============================
+// CONCRETE CONTEXT
+// ==============================
+
+class Computer {
+    constructor() {
+        this._currentState = null;
+        this._states = {
+            off: new Off(),
+            on: new On()
+        };
+    }
+
+    power() {
+        this._currentState.power(this); 
+    }
+
+    getCurrentState() {
+        return this._currentState; 
+    }
+
+    setCurrentState(state) {
+        this._currentState = state; 
+    }
+
+    getStates() {
+        return this._states; 
+    }
+}
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+let pc = new Computer();
+
+pc.setCurrentState(pc.getStates().off);
+
+console.log(pc.getCurrentState().constructor.name); // Off
+pc.power();
+console.log(pc.getCurrentState().constructor.name); // On
+pc.power();
+console.log(pc.getCurrentState().constructor.name); // Off