并行继承链中的多态性和类型安全性 [英] Polymorphism AND type safety in parallel inheritance chains

问题描述

我有两个并行继承链：

  Chain1：
动物<  -  Lion 
< ;  -  Gazelle 
 
 Chain2：
 Food < -  Meat 
 < -  Grass 
  

我想在Animal上实现Eats多态属性。这是它的样子：

  public abstract class Animal 
 {
 public abstract Food Eats {get ; set;} 
} 
 
 
公共类Lion：Animal 
 {
 public override Food Eats 
 {
 get {return新的Meat（）;} 
 set 
 {
 if（value is Meat）DoSomething（value）; 
另外抛出新的异常（狮子只吃肉。+ 
你最好学习这个，老兄！）; 
} 
} 
} 
  

然而，这段代码并不是类型安全。我应该用草喂狮子吗，我只会在运行时遇到我的bug。

有人可以给我提供一个代码示例，它有助于在不牺牲多态性的情况下使用泛型进行类型安全吗？

解决动物可以是一个泛型类：

  public abstract class Animal< T> T：食物
 {
 public abstract T Eats {get; set;} 
} 
  

然后你可以让狮子成为这样的肉食动物

  public class Lion：Animal< Meat> 
 {
 //等等... 
} 
  

但是这不是一个最佳解决方案。你不能再使用动物作为多态接口，因为你需要知道使用它的细节。这可能不是多态的地方。

I have two parallel inheritance chains:

Chain1:
Animal <- Lion
       <- Gazelle

Chain2:
Food   <- Meat
       <- Grass

I want to implement the "Eats" polymorphic property on Animal. This is how it looks like:

public abstract class Animal
{
  public abstract Food Eats { get; set;}
}


public class Lion : Animal
{
  public override Food Eats
  {
     get { return new Meat();}
     set 
     {
       if (value is Meat) DoSomething(value);
       else throw new Exception("Lions only eat meat. " + 
                                "You better learn that, dude!");
     }
  }
}

However, this code is not type safe. Should I feed my Lion with grass, I will be confronted with my bug only in runtime.

Could someone provide me with a code example that facilitates type safety using Generics without sacrificing polymorphism?

解决方案

Animal can be a generic class:

public abstract class Animal<T> where T : Food
{
    public abstract T Eats {get;set;}
}

then you can make lion a meat eating animal like this

public class Lion : Animal<Meat>
{
    //etc...
}    

But this is not be an optimal solution. You can't use animal as a polymorphic interface any more because you need to know details about it's implementation to use it. This might just not be the place for polymorphism.

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