设计模式之装饰者模式，奶茶店场景

// See https://aka.ms/new-console-template for more information
using System.Drawing;

/*
　　装饰者模式，不改变实现类的情况下，动态给实现类增加新功能，这里使用聚合关系实现

    奶茶店
    实现点奶茶加不同的料，计算价格的场景，使用装饰者模式实现

    优点，新增一种小料时只需要实现IDecorator接口即可扩展，符合开闭原则
 */

var beverage = new MilkTea();   //先点一杯奶茶
beverage.Add(new Pudding());    //加一份布丁
beverage.Add(new Boba());      //加一份珍珠

Console.WriteLine($"Hello, World {beverage.Cost()}");  //算出价格 


/// <summary>
/// 饮料基类
/// </summary>
abstract class Beverage
{
    protected readonly List<IDecorator> decorators;  //聚合多种小料
    public Beverage()
    {
        decorators = new List<IDecorator>();
    }

    public void Add(IDecorator decorator)
    {
        decorators.Add(decorator);
    }

    public abstract double Cost();
}

/// <summary>
/// 奶茶
/// </summary>
class MilkTea : Beverage
{
    private double PRICE = 15;
    public override double Cost()
    {
        return PRICE + decorators.Sum(s => s.Price);
    }
}

/// <summary>
/// 水果茶
/// </summary>
class FruitTea : Beverage
{
    private double PRICE = 20;
    public override double Cost()
    {
        return PRICE + decorators.Sum(s => s.Price);
    }
}

/// <summary>
/// 小料接口（装饰者）
/// </summary>
interface IDecorator
{
    double Price { get; set; }
}

/// <summary>
/// 布丁   3元一份
/// </summary>
class Pudding : IDecorator
{
    public double Price { get; set; } = 3;
}

/// <summary>
/// 珍珠 两元一份
/// </summary>
class Boba : IDecorator
{
    public double Price { get; set; } = 2;
}