c# - 以下代码如何调用 Equals、GetHashCode 和 Compare？ (神秘)

Question

此代码有效，但它如何不实际调用任何列出的方法。它有效，但它的工作原理和原因似乎几乎是神奇的。我实际上从未调用过 Equals、GetHashCode 或 Compare，但代码有效。我也从不在实现两个接口(interface)的 EmployeeComparer 类的构造函数中调用任何东西。

问题:这是在使用新关键字实例化类时自动完成的吗？(这里似乎有些不对劲)

        public class EmployeeComparer : IEqualityComparer<Employee>,
                                        IComparer<Employee>

员工比较器:

        public bool Equals(Employee x, Employee y)
        {
            return String.Equals(x.Name, y.Name);
        }

        public int GetHashCode(Employee obj)
        {
            return obj.Name.GetHashCode();
        }

        public int Compare(Employee x, Employee y)
        {
            return String.Compare(x.Name, y.Name);
        }

类:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        public delegate void Del(string e);
        Del handler = DelegateMethod;
        Dictionary<string, List<Employee>> d = new Dictionary<string, 
                                                              List<Employee>>();

        public static void DelegateMethod(string message)
        {
            System.Console.WriteLine(message);
            System.Console.ReadKey();
        }

        public void testDel(Del d)
        {
            d.Invoke("L");
        }

        static void Main(string[] args)
        {
            Program p = new Program();
            //p.handler("Hello World");
            //p.handler("DisneyLand");
            //p.handler("Cattle Wars");
            //p.testDel(p.handler);
            var d = new SortedDictionary<string, SortedSet<Employee>>();
                                                               //Hashset no duplicates

            d.Add("AA", new SortedSet<Employee>(new EmployeeComparer()));
            d["AA"].Add(new Employee { Name = "A" });
            d["AA"].Add(new Employee { Name = "B"} );
            d["AA"].Add(new Employee { Name = "C"} );
            d["AA"].Add(new Employee { Name = "C" });
            d["AA"].Add(new Employee { Name = "C" });

            d.Add("BB", new SortedSet<Employee>(new EmployeeComparer()));
            d["BB"].Add(new Employee { Name = "E"} );
            d["BB"].Add(new Employee { Name = "F"} );
            d["BB"].Add(new Employee { Name = "A"} );

            d.Add("CC", new SortedSet<Employee>(new EmployeeComparer()));
            d["CC"].Add(new Employee { Name = "Z"} );
            d["CC"].Add(new Employee { Name = "X"} );
            d["CC"].Add(new Employee { Name = "Y"} );

            d.Add("DD", new SortedSet<Employee>(new EmployeeComparer()));
            d["DD"].Add(new Employee { Name = "Z" });
            d["DD"].Add(new Employee { Name = "U" });
            d["DD"].Add(new Employee { Name = "U" });
            d["DD"].Add(new Employee { Name = "Q" });
            d["DD"].Add(new Employee { Name = "Y" });

            foreach (var a in d)
            {
                Console.WriteLine(a.Key);
                foreach (var e in a.Value)
                {
                    Console.WriteLine("\t" + e.Name);
                }
            }
            Console.ReadKey();
        }
    }

    public class EmployeeComparer : IEqualityComparer<Employee>, 
                                    IComparer<Employee>
    {
        public EmployeeComparer() { }

        public bool Equals(Employee x, Employee y)
        {
            return String.Equals(x.Name, y.Name);
        }

        public int GetHashCode(Employee obj)
        {
            return obj.Name.GetHashCode();
        }

        public int Compare(Employee x, Employee y)
        {
            return String.Compare(x.Name, y.Name);
        }
    }
}

Answer 1

这根本不是魔法。 SortedSet<T> 的实现调用 Compare (在您的示例中，没有调用 GetHashCode 或 Equals )。就像您执行以下操作一样:

void Main()
{
    MyMethod(new EmployeeComparer());
}
void MyMethod(IComparer<Employee> comparer)
{
    var emp1 = new Employee { Name = "George" };
    var emp2 = new Employee { Name = "Tom" };
    Console.WriteLine(comparer.Compare(emp1, emp2));
}

来自 Main的角度来看，它从未调用过Compare , 它只做了一个 new .它调用的方法是执行 Compare 的方法。 .