usingSystem;// Extension methods must be parts of static classes.staticclassBooleanExtensionMethodSample{publicstaticvoidMain(){boolyes=true;boolno=false;// Toggle the booleans! yes should return false and no should return true.Console.WriteLine(yes.Toggle());Console.WriteLine(no.Toggle());}// The extension method that adds Toggle to bool.publicstaticboolToggle(thisbooltarget){// Return the opposite of the target.return!target;}}

Coffee making scenario

#include<iostream>#include<string>// The abstract coffee classclassCoffee{public:virtualdoublegetCost()=0;virtualstd::stringgetIngredient()=0;virtual~Coffee(){}};// Plain coffee without ingredientclassSimpleCoffee:publicCoffee{private:doublecost;std::stringingredient;public:SimpleCoffee(){cost=1;ingredient=std::string("Coffee");}doublegetCost(){returncost;}std::stringgetIngredient(){returningredient;}};// Abstract decorator classclassCoffeeDecorator:publicCoffee{protected:Coffee&decoratedCoffee;public:CoffeeDecorator(Coffee&decoratedCoffee):decoratedCoffee(decoratedCoffee){}~CoffeeDecorator(){delete&decoratedCoffee;}};// Milk DecoratorclassMilk:publicCoffeeDecorator{private:doublecost;public:Milk(Coffee&decoratedCoffee):CoffeeDecorator(decoratedCoffee){cost=0.5;}doublegetCost(){returncost+decoratedCoffee.getCost();}std::stringgetIngredient(){return"Milk "+decoratedCoffee.getIngredient();}};// Whip decoratorclassWhip:publicCoffeeDecorator{private:doublecost;public:Whip(Coffee&decoratedCoffee):CoffeeDecorator(decoratedCoffee){cost=0.7;}doublegetCost(){returncost+decoratedCoffee.getCost();}std::stringgetIngredient(){return"Whip "+decoratedCoffee.getIngredient();}};// Sprinkles decoratorclassSprinkles:publicCoffeeDecorator{private:doublecost;public:Sprinkles(Coffee&decoratedCoffee):CoffeeDecorator(decoratedCoffee){cost=0.6;}doublegetCost(){returncost+decoratedCoffee.getCost();}std::stringgetIngredient(){return"Sprinkles "+decoratedCoffee.getIngredient();}};// Here's a testintmain(){Coffee*sample;sample=newSimpleCoffee();sample=newMilk(*sample);sample=newWhip(*sample);std::cout<<sample->getIngredient()<<std::endl;std::cout<<"Cost: "<<sample->getCost()<<std::endl;deletesample;}

// Class to be decoratedfunctionCoffee(){this.cost=function(){return1;};}// Decorator AfunctionMilk(coffee){this.cost=function(){returncoffee.cost()+0.5;};}// Decorator BfunctionWhip(coffee){this.cost=function(){returncoffee.cost()+0.7;};}// Decorator CfunctionSprinkles(coffee){this.cost=function(){returncoffee.cost()+0.2;};}// Here's one way of using itvarcoffee=newMilk(newWhip(newSprinkles(newCoffee())));alert(coffee.cost());// Here's anothervarcoffee=newCoffee();coffee=newSprinkles(coffee);coffee=newWhip(coffee);coffee=newMilk(coffee);alert(coffee.cost());

funprintInfo(c:Coffee){println("Cost: "+c.cost+"; Ingredients: "+c.ingredients)}funmain(args:Array<String>){varc:Coffee=SimpleCoffee()printInfo(c)c=WithMilk(c)printInfo(c)c=WithSprinkles(c)printInfo(c)}// The interface Coffee defines the functionality of Coffee implemented by decoratorinterfaceCoffee{valcost:Double// Returns the cost of the coffeevalingredients:String// Returns the ingredients of the coffee}// Extension of a simple coffee without any extra ingredientsclassSimpleCoffee:Coffee{overridevalcost:Doubleget()=1.0overridevalingredients:Stringget()="Coffee"}// Abstract decorator class - note that it implements Coffee interfaceabstractclassCoffeeDecorator(privatevaldecoratedCoffee:Coffee):Coffee{override// Implementing methods of the interfacevalcost:Doubleget()=decoratedCoffee.costoverridevalingredients:Stringget()=decoratedCoffee.ingredients}// Decorator WithMilk mixes milk into coffee.// Note it extends CoffeeDecorator.classWithMilk(c:Coffee):CoffeeDecorator(c){override// Overriding methods defined in the abstract superclassvalcost:Doubleget()=super.cost+0.5overridevalingredients:Stringget()=super.ingredients+", Milk"}// Decorator WithSprinkles mixes sprinkles onto coffee.// Note it extends CoffeeDecorator.classWithSprinkles(c:Coffee):CoffeeDecorator(c){overridevalcost:Doubleget()=super.cost+0.2overridevalingredients:Stringget()=super.ingredients+", Sprinkles"}

First Example (window/scrolling scenario)

// the Window abstract classpublicabstractclassWindow{publicabstractvoiddraw();// draws the WindowpublicabstractStringgetDescription();// returns a description of the Window}// extension of a simple Window without any scrollbarsclassSimpleWindowextendsWindow{publicvoiddraw(){// draw window}publicStringgetDescription(){return"simple window";}}

// abstract decorator class - note that it extends WindowabstractclassWindowDecoratorextendsWindow{protectedWindowdecoratedWindow;// the Window being decoratedpublicWindowDecorator(WindowdecoratedWindow){this.decoratedWindow=decoratedWindow;}publicvoiddraw(){decoratedWindow.draw();//delegation}publicStringgetDescription(){returndecoratedWindow.getDescription();//delegation}}// the first concrete decorator which adds vertical scrollbar functionalityclassVerticalScrollBarDecoratorextendsWindowDecorator{publicVerticalScrollBarDecorator(WindowdecoratedWindow){super(decoratedWindow);}@Overridepublicvoiddraw(){super.draw();drawVerticalScrollBar();}privatevoiddrawVerticalScrollBar(){// draw the vertical scrollbar}@OverridepublicStringgetDescription(){returnsuper.getDescription()+", including vertical scrollbars";}}// the second concrete decorator which adds horizontal scrollbar functionalityclassHorizontalScrollBarDecoratorextendsWindowDecorator{publicHorizontalScrollBarDecorator(WindowdecoratedWindow){super(decoratedWindow);}@Overridepublicvoiddraw(){super.draw();drawHorizontalScrollBar();}privatevoiddrawHorizontalScrollBar(){// draw the horizontal scrollbar}@OverridepublicStringgetDescription(){returnsuper.getDescription()+", including horizontal scrollbars";}}

publicclassDecoratedWindowTest{publicstaticvoidmain(String[]args){// create a decorated Window with horizontal and vertical scrollbarsWindowdecoratedWindow=newHorizontalScrollBarDecorator(newVerticalScrollBarDecorator(newSimpleWindow()));// print the Window's descriptionSystem.out.println(decoratedWindow.getDescription());}}

Second Example (coffee making scenario)

// The abstract Coffee class defines the functionality of Coffee implemented by decoratorpublicabstractclassCoffee{publicabstractdoublegetCost();// returns the cost of the coffeepublicabstractStringgetIngredients();// returns the ingredients of the coffee}// extension of a simple coffee without any extra ingredientspublicclassSimpleCoffeeextendsCoffee{publicdoublegetCost(){return1;}publicStringgetIngredients(){return"Coffee";}}

// abstract decorator class - note that it extends Coffee abstract classpublicabstractclassCoffeeDecoratorextendsCoffee{protectedfinalCoffeedecoratedCoffee;protectedStringingredientSeparator=", ";publicCoffeeDecorator(CoffeedecoratedCoffee){this.decoratedCoffee=decoratedCoffee;}publicdoublegetCost(){// implementing methods of the abstract classreturndecoratedCoffee.getCost();}publicStringgetIngredients(){returndecoratedCoffee.getIngredients();}}// Decorator Milk that mixes milk with coffee// note it extends CoffeeDecoratorclassMilkextendsCoffeeDecorator{publicMilk(CoffeedecoratedCoffee){super(decoratedCoffee);}publicdoublegetCost(){// overriding methods defined in the abstract superclassreturnsuper.getCost()+0.5;}publicStringgetIngredients(){returnsuper.getIngredients()+ingredientSeparator+"Milk";}}// Decorator Whip that mixes whip with coffee// note it extends CoffeeDecoratorclassWhipextendsCoffeeDecorator{publicWhip(CoffeedecoratedCoffee){super(decoratedCoffee);}publicdoublegetCost(){returnsuper.getCost()+0.7;}publicStringgetIngredients(){returnsuper.getIngredients()+ingredientSeparator+"Whip";}}// Decorator Sprinkles that mixes sprinkles with coffee// note it extends CoffeeDecoratorclassSprinklesextendsCoffeeDecorator{publicSprinkles(CoffeedecoratedCoffee){super(decoratedCoffee);}publicdoublegetCost(){returnsuper.getCost()+0.2;}publicStringgetIngredients(){returnsuper.getIngredients()+ingredientSeparator+"Sprinkles";}}

publicclassMain{publicstaticfinalvoidmain(String[]args){Coffeec=newSimpleCoffee();System.out.println("Cost: "+c.getCost()+"; Ingredients: "+c.getIngredients());c=newMilk(c);System.out.println("Cost: "+c.getCost()+"; Ingredients: "+c.getIngredients());c=newSprinkles(c);System.out.println("Cost: "+c.getCost()+"; Ingredients: "+c.getIngredients());c=newWhip(c);System.out.println("Cost: "+c.getCost()+"; Ingredients: "+c.getIngredients());// Note that you can also stack more than one decorator of the same typec=newSprinkles(c);System.out.println("Cost: "+c.getCost()+"; Ingredients: "+c.getIngredients());}}

Window System

# the Window base classclassWindow(object):defdraw(self,device):device.append('flat window')definfo(self):pass# The decorator pattern approchclassWindowDecorator:def__init__(self,w):self.window=wdefdraw(self,device):self.window.draw(device)definfo(self):self.window.info()classBorderDecorator(WindowDecorator):defdraw(self,device):self.window.draw(device)device.append('borders')classScrollDecorator(WindowDecorator):defdraw(self,device):self.window.draw(device)device.append('scroll bars')deftest_deco():# The way of using the decorator classesw=ScrollDecorator(BorderDecorator(Window()))dev=[]w.draw(dev)printdevtest_deco()

Difference between subclass method and decorator pattern

# The subclass approchclassBorderedWindow(Window):defdraw(self,device):super(BorderedWindow,self).draw(device)device.append('borders')classScrolledWindow(Window):defdraw(self,device):super(ScrolledWindow,self).draw(device)device.append('scroll bars')# combine the functionalities using multiple inheritance.classMyWindow(ScrolledWindow,BorderedWindow,Window):passdeftest_muli():w=MyWindow()dev=[]w.draw(dev)printdevdeftest_muli2():# note that python can create a class on the fly.MyWindow=type('MyWindow',(ScrolledWindow,BorderedWindow,Window),{})w=MyWindow()dev=[]w.draw(dev)printdevtest_muli()test_muli2()

Coffee example

typeCoffee()=abstractmemberCost:doubleabstractmemberIngredients:stringlistdefaultthis.Cost=1.0defaultthis.Ingredients=["Coffee"]typeCoffeeDecorator(coffee:Coffee)=inheritCoffee()overridethis.Cost=coffee.Costoverridethis.Ingredients=coffee.IngredientstypeWithMilk(coffee:Coffee)=inheritCoffeeDecorator(coffee)overridethis.Cost=base.Cost+0.5overridethis.Ingredients=["Milk"]|>List.appendbase.IngredientstypeWithSprinkles(coffee:Coffee)=inheritCoffeeDecorator(coffee)overridethis.Cost=base.Cost+0.2overridethis.Ingredients=["Sprinkles"]|>List.appendbase.Ingredientsletprint(coffee:Coffee)=printfn"Cost: %.2f$; Ingredients: %A"coffee.Costcoffee.IngredientsletwithAddins=Coffee()|>WithMilk|>WithSprinklesprintwithAddins