重构第四天 : 用多态替换条件语句（if else & switch)

面相对象的一个核心基础就是多态，当你要根据对象类型的不同要做不同的操作的时候，一个好的办法就是采用多态，把算法封装到子类当中去。

重构前代码：

public abstract class Customer
{
}
  
public class Employee : Customer
{
}
  
public class NonEmployee : Customer
{
}
  
public class OrderProcessor
{
     public decimal ProcessOrder(Customer customer, IEnumerable<Product> products)
     {
         // do some processing of order
         decimal orderTotal = products.Sum(p => p.Price);
  
         Type customerType = customer.GetType();
         if (customerType == typeof(Employee))
         {
             orderTotal -= orderTotal * 0.15m;
         }
         else if (customerType == typeof(NonEmployee))
         {
             orderTotal -= orderTotal * 0.05m;
         }
  
         return orderTotal;
     }
}

重构后的代码：

public abstract class Customer
  {
      public abstract decimal DiscountPercentage { get; }
  }
   
  public class Employee : Customer
  {
      public override decimal DiscountPercentage
      {
          get { return 0.15m; }
      }
  }
   
  public class NonEmployee : Customer
  {
      public override decimal DiscountPercentage
      {
          get { return 0.05m; }
      }
  }
   
  public class OrderProcessor
  {
      public decimal ProcessOrder(Customer customer, IEnumerable<Product> products)
      {
          // do some processing of order
          decimal orderTotal = products.Sum(p => p.Price);
   
          orderTotal -= orderTotal * customer.DiscountPercentage;
   
          return orderTotal;
      }
  }