Question

我最近问过这个问题：When would == be overridden in a different way to .equals?。我被引用到这篇文章：https://ericlippert.com/2013/10/07/math-from-scratch-part-six-comparisons/

我不完全理解对静态方法调用（==和!=）和动态方法调用（.Equals()）的引用。请参阅以下代码：

public class A
{
    private string Field1;
    private string Field2;

    public A(string field1, string field2)
    {
        Field1 = field1;
        Field2 = field2;
    }

    public static bool operator ==(A a1, A a2)
    {
        throw new NotImplementedException();
    }

    public static bool operator !=(A a1, A a2b)
    {
        throw new NotImplementedException();
    }

    public override int GetHashCode()
    {
        throw new NotImplementedException();
    }

    public override bool Equals(object obj)
    {
        throw new NotImplementedException();
    }
}

public class B : A
{
    private string Field3;
    private string Field4;

    public B(string field1, string field2, string field3, string field4)
        : base(field1, field2)
    {
        Field3 = field3;
        Field4 = field4;
    }

    public static bool operator ==(B a1, B a2)
    {
        throw new NotImplementedException();
    }

    public static bool operator !=(B a1, B a2b)
    {
        throw new NotImplementedException();
    }

    public override int GetHashCode()
    {
        throw new NotImplementedException();
    }

    public override bool Equals(object obj)
    {
        throw new NotImplementedException();
    }
}

以及下面的测试：

A a1 = new B("hello","hello","hello","hello");
A a2 = new B("hello", "hello", "hello", "hello");
var test1 = a1.Equals(a2);
var test2 = a1 == a2;

我不明白它以这种方式实现的原因？我今天晚上花了最后一小时用Google搜索，但是我仍然不清楚这个问题的原因。为什么动态调度.Equals()并静态调度==？

Answer 1

df %>% mutate(newCol = replace(newCol, `last name` %in% c("a", "c", "e"), "No"))是一个虚拟实例方法，受普通覆盖规则/多态性的约束。

.Equals()是静态==方法的语法糖，这是一个带有两个参数的普通静态方法调用，因此根本不进行动态调度。

为什么动态调度.Equals（）并静态调度==？

1 个答案: