操作符重载和继承C＃

问题描述：

比方说，我有一个父类和子类，如下操作符重载和继承C＃

父类：

class Parent 
{ 
    public string _First; 
    public string _Last; 

    public override bool Equals(object obj) 
    { 
     if (ReferenceEquals(obj, null)) 
      return false; 
     else if (ReferenceEquals(obj, this)) 
      return true; 
     else if (obj is Parent == false) 
      return false; 
     else 
      return this.Equals(obj as Parent) & base.Equals(obj); 

    } 

    public override int GetHashCode() 
    { 
     unchecked 
     { 
      return this._First.GetHashCode()^this._Last.GetHashCode()^base.GetHashCode(); 
     } 
    } 

    public bool Equals(Parent that) 
    { 
     if (ReferenceEquals(that, null)) 
      return false; 
     else if (ReferenceEquals(that, this)) 
      return true; 
     else 
      return this._First.Equals(that._First) & this._Last.Equals(that._Last); 
    } 

    public static bool operator ==(Parent p1, Parent p2) 
    { 
     return p1.Equals(p2); 
    } 

    public static bool operator !=(Parent p1, Parent p2) 
    { 
     return !p1.Equals(p2); 
    } 


}

子类：

class Child : Parent 
{ 
    public string Address; 

    public override bool Equals(object obj) 
    { 
     if (ReferenceEquals(obj, null)) 
      return false; 
     else if (ReferenceEquals(obj, this)) 
      return true; 
     else if (obj is Parent == false) 
      return false; 
     else 
      return this.Equals(obj as Child); 

    } 

    public override int GetHashCode() 
    { 
     unchecked 
     { 
      return this._First.GetHashCode()^this._Last.GetHashCode()^base.GetHashCode(); 
     } 
    } 

    public bool Equals(Child that) 
    { 
     if (ReferenceEquals(that, null)) 
      return false; 
     else if (ReferenceEquals(that, this)) 
      return true; 
     else 
      return this.Address.Equals(that.Address) & base.Equals(that); 
    } 

    public static bool operator ==(Child p1,Child p2) 
    { 
     return p1.Equals(p2); 
    } 

    public static bool operator !=(Child p1, Child p2) 
    { 
     return !p1.Equals(p2); 
    } 

}

这里是代码比较两个孩子的情况。

Parent p = new Child() { _First = "Mitul", _Last = "Patel", Address="abc1"}; 
     Parent p1 = new Child() { _First = "Mitul", _Last = "Patel", Address = "abc" }; 

     Child c = new Child() { _First = "Mitul", _Last = "Patel", Address = "abc1" }; 
     Child c1 = new Child() { _First = "Mitul", _Last = "Patel", Address = "abc" }; 

     Console.WriteLine(p.Equals(p1)); 
     Console.WriteLine(p == p1); 

     Console.WriteLine(c.Equals(c1)); 
     Console.WriteLine(c == c1); 

     Console.Read();

输出

真真假假

我知道为什么第一个比较过程中提供真正的和真实的。因为它调用父类的重载==（）运算符。我的问题是我想使用子类的==操作符，因为对象是Child类型，所以它怎么可能？对于静态方法，virtual关键字不能使用。

谢谢，

答

在编译时选择运算符的实现。运算符不是虚方法 - 子类的==运算符不会覆盖父类==运算符。因此，编译器选择子操作符==的唯一方法是让变量本身的类型为Child，例如，

Child p = new Child() { _First = "Mitul", _Last = "Patel", Address="abc1"}; 
Child p1 = new Child() { _First = "Mitul", _Last = "Patel", Address = "abc" };

或有==操作员呼叫Equals方法，使的Equals的儿童实现覆盖父类的实现：

在Parent.cs

：

// No need for these to be public- they should only be called internally. 
protected virtual bool Equals(Parent that) 
{ 
    if (ReferenceEquals(that, null)) 
     return false; 
    else if (ReferenceEquals(that, this)) 
     return true; 
    else 
     return this._First.Equals(that._First) & this._Last.Equals(that._Last); 
}

在Child.cs ：

// Notice I changed your argument type here... 
protected override bool Equals(Parent that) 
{ 
    // If we are not dealing with a Child instance, delegate to the base class. 
    if (!(that is typeof(Child))) 
     return base.Equals(that); 

    if (ReferenceEquals(that, null)) 
     return false; 
    else if (ReferenceEquals(that, this)) 
     return true; 
    else 
     return this.Address.Equals(that.Address) & base.Equals(that); 
}

谢谢克里斯。是的，这有意义使Equals方法在父项中是虚拟的。 – mchicago

答

static方法在co mpile时间，而不是在运行时间。
对于您的代码p和p1是Parent对象，所以它会调用Parent类的==运算符。
如果您希望调用派生类的运算符，则必须将它们声明为派生类实例。

操作符重载和继承C＃

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