swift - The Decorator Pattern

装饰者模式：多个类派生于一个基础类，这几个类可以嵌套构造来装饰。

client:

let account =CustomerAccount(name:"Joe");

account.addPurchase(Purchase(product:"Red Hat",price: 10));

account.addPurchase(Purchase(product:"Scarf",price: 20));

account.addPurchase(EndOfLineDecorator(purchase:BlackFridayDecorator(purchase:

GiftOptionDecorator(purchase: Purchase(product: "Sunglasses",price:25),

options:GiftOptionDecorator.OPTION.GIFTWRAP,

GiftOptionDecorator.OPTION.DELIVERY))));

account.printAccount();

for p inaccount.purchases {

iflet d = p as? DiscountDecorator {

println("(p) has(d.countDiscounts()) discounts");

}else {

println("(p) has no discounts");

}

}

pattern:

class Purchase :Printable {

private let product:String;

private let price:Float;

init(product:String,price:Float) {

self.product = product;

self.price = price;

}

var description:String {

return product;

}

var totalPrice:Float {

return price;

}

}

class GiftOptionDecorator :Purchase {

private let wrappedPurchase:Purchase;

private let options:[OPTION];

enum OPTION {

case GIFTWRAP;

case RIBBON;

case DELIVERY;

}

init(purchase:Purchase,options:OPTION...) {

self.wrappedPurchase = purchase;

self.options = options;

super.init(product: purchase.description,price: purchase.totalPrice);

}

override var description:String {

var result =wrappedPurchase.description;

for option inoptions {

switch (option) {

case .GIFTWRAP:

result ="(result) + giftwrap";

case .RIBBON:

result ="(result) + ribbon";

case .DELIVERY:

result ="(result) + delivery";

}

}

return result;

}

override var totalPrice:Float {

var result =wrappedPurchase.totalPrice;

for option inoptions {

switch (option) {

case .GIFTWRAP:

result +=2;

case .RIBBON:

result +=1;

case .DELIVERY:

result +=5;

}

}

return result;

}

}

class DiscountDecorator:Purchase {

private let wrappedPurchase:Purchase;

init(purchase:Purchase) {

self.wrappedPurchase = purchase;

super.init(product: purchase.description,price: purchase.totalPrice);

}

override var description:String {

return super.description;

}

var discountAmount:Float {

return 0;

}

func countDiscounts() -> Int {

var total = 1;

if let discounter =wrappedPurchase as?DiscountDecorator {

total += discounter.countDiscounts();

}

return total;

}

}

class BlackFridayDecorator :DiscountDecorator {

override var totalPrice:Float {

returnsuper.totalPrice -discountAmount;

}

override var discountAmount:Float {

return super.totalPrice *0.20;

}

}

class EndOfLineDecorator :DiscountDecorator {

override var totalPrice:Float {

returnsuper.totalPrice -discountAmount;

}

override var discountAmount:Float {

return super.totalPrice *0.70;

}

}

import Foundation

class CustomerAccount {

let customerName:String;

var purchases = [Purchase]();

init(name:String) {

self.customerName = name;

}

func addPurchase(purchase:Purchase) {

self.purchases.append(purchase);

}

func printAccount() {

var total:Float =0;

for p in purchases {

total += p.totalPrice;

println("Purchase(p),Price(formatCurrencyString(p.totalPrice))");

}

println("Total due:(formatCurrencyString(total))");

}

func formatCurrencyString(number:Float) ->String {

let formatter = NSNumberFormatter();

formatter.numberStyle =NSNumberFormatterStyle.CurrencyStyle;

return formatter.stringFromNumber(number) ??"";

}

}

（编辑：李大同）

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