运算符重载和继承 C#
本文关键字:继承 重载 运算符 | 更新日期: 2023-09-27 18:33:51
假设我有一个父类和子类,如下所示
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);
}
}
儿童班:
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);
}
}
这是比较两个孩子实例的代码。
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
我知道为什么它在第一次比较时给出真实和真实。因为它调用了父类的重载 ==() 运算符。我的问题是我想使用子类的 == 运算符,因为对象是 Child 类型,所以怎么可能?对于静态方法,不能使用虚拟关键字。
谢谢
运算符的实现是在编译时选择的。 运算符不是虚拟方法 - 子类的==
运算符不会覆盖父类==
运算符。
因此,使编译器选择子==
运算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" };
或者让 ==
运算符调用 Equals 方法,并使 Equals 的子实现覆盖父实现:
在父.cs中:
// 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);
}
在儿童.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);
}
static
方法在编译时解析,而不是在运行时解析。
对于您的代码,p
和p1
是Parent
对象,因此它将调用 Parent
类的 ==
运算符。
如果要调用派生类的运算符,则必须将它们声明为派生类实例。