如何在 HashCode 中包含 "joker" 值

Question

我有下面的例子class:

public sealed class MyDictKey
{
    public int Type { get; }
    public int SubType { get; }

    public MyDictKey(int type, int subType) // both can only be positive values
    {
        Type = type;
        SubType = subType;
    }

    public override bool Equals(object obj)
    {
        if (obj is MyDictKey other)
        {
            bool typeEqual = other.Type == Type;
            bool subTypeEqual = other.SubType == -1 || SubType == -1 || other.SubType == SubType;
            return typeEqual && subTypeEqual;
        }

        return false;
    }

    public override int GetHashCode()
    {
        unchecked
        {
            int hash = 17;
            hash = hash * 23 + Type.GetHashCode();
            return hash;
        }
    }
}

和下面的测试（NUnit，如果有人感兴趣的话）：

    [Test]
    public void CalculatorTest()
    {
        Dictionary<MyDictKey, string> myTypeProcessors = new Dictionary<MyDictKey, string>();

        myTypeProcessors.Add(new MyDictKey(10, 20), "10.20_processor");
        myTypeProcessors.Add(new MyDictKey(3, 4), "3.4_processor");
        myTypeProcessors.Add(new MyDictKey(4, -1), "4.any_processor");
        // -1 means it can process "any" subtype

        for (int i = 0; i < 1000; i++) // should work for any positive number
        {
            bool canGet = myTypeProcessors.TryGetValue(new MyDictKey(4, i), out string value);
            Assert.IsTrue(canGet);
            Assert.That(value, Is.EqualTo("4.any_processor"));

            bool canGet2 = myTypeProcessors.TryGetValue(new MyDictKey(10, i), out string value2);
            if (i == 20)
            {
                Assert.IsTrue(canGet2);
                Assert.That(value2, Is.EqualTo("10.20_processor"));
            }
            else
            {
                Assert.IsFalse(canGet2);
            }
        }
    }

我能否仅通过使用 GetHashCode 以某种方式达到相同的机制？ 因为这样，如果只有 SubType 不同，字典的 TryGetValue 将始终调用 Equals 方法。重要的是新方法一定不能比原来的慢。

我在想按位运算符；或者有什么神奇的数学公式吗？

提前致谢。

Answer 1

这甚至不是一个定义明确的等式函数，因为它不能传递。

EG A=(1,1), B =(1,-1), C=(1,2)

A=B，B=C，但不是 A=C

考虑：

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

    namespace ConsoleApp5
    {
        class Program
        {
            static void Main(string[] args)
            {
                var A = new MyDictKey(1, 1);
                var B = new MyDictKey(1, -1);
                var C = new MyDictKey(1, 2);

                var h = new HashSet<MyDictKey>();
                h.Add(A);
                h.Add(B);
                h.Add(C);
                Console.WriteLine(h.Count); //outputs 2


                var h2 = new HashSet<MyDictKey>();
                h2.Add(B);
                h2.Add(C);
                h2.Add(A);
                Console.WriteLine(h2.Count); //outputs 1

                Console.ReadKey();

            }

            public sealed class MyDictKey
            {
                public int Type { get; }
                public int SubType { get; }

                public MyDictKey(int type, int subType) // both can only be positive values
                {
                    Type = type;
                    SubType = subType;
                }

                public override bool Equals(object obj)
                {
                    if (obj is MyDictKey other)
                    {
                        bool typeEqual = other.Type == Type;
                        bool subTypeEqual = other.SubType == -1 || SubType == -1 || other.SubType == SubType;
                        return typeEqual && subTypeEqual;
                    }

                    return false;
                }

                public override int GetHashCode()
                {
                    unchecked
                    {
                        int hash = 17;
                        hash = hash * 23 + Type.GetHashCode();
                        return hash;
                    }
                }
            }
        }
    }

如何在 HashCode 中包含 "joker" 值

How to include a "joker" value in HashCode

.net

c#

gethashcode