c# 中的运行时类型重载

Question

考虑以下代码：

public class A
{
    public A(){}
}

public class B:A
{
    public B(){}
}

public class C
{
    public C(){}
    
    public void fun(A a)
    {
        Console.WriteLine("that was A");
    }
    
    public void fun(B b)
    {
        Console.WriteLine("that was B");
    }
}

public class Program
{
    public static void Main()
    {
        A a = new A(), b = new B();
        C c = new C();
        c.fun(a);
        c.fun(b);
    }
}

在当前形式中，它说"that was A"两次。 如何修复 class C ，以便在b的运行时类型为B时调用fun(B b) ，但编译类型为A ？ 目前它只有在我在编译期间将b声明为B时才能正常工作。

@Edit：不使用if等检查类型。

Answer 1

通过虚拟方法调用fun 。

public class A
{
    public virtual void fun(C c) 
    {
        c.fun(this);
    }
}

public class B:A
{
    public override void fun(C c) 
    {
        c.fun(this);
    }
}

public class C
{
    public void fun(A a)
    {
        Console.WriteLine("that was A");
    }

    public void fun(B b)
    {
        Console.WriteLine("that was B");
    }
}

public class Program
{
    public static void Main()
    {
        A a = new A(), b = new B();
        C c = new C();
        a.fun(c);
        b.fun(c);
    }
}

Output：

that was A
that was B

请参阅小提琴上的示例