EqualityComparer for KeyValuePair的问题

Question

我在KeyValuePair中有一个类，IEquatable的实现不像我预期的那样工作。我的单元测试失败了。我想知道为什么测试失败？

类：

public class MyClass : IEquatable<MyClass>
{
    public KeyValuePair<int[], string> KeyValuePair { get; set; }

    public override bool Equals(object obj)
    {
        return Equals(obj as MyClass);
    }

    public bool Equals(MyClass other)
    {
        return other != null &&
               EqualityComparer<KeyValuePair<int[], string>>.Default.Equals(KeyValuePair, other.KeyValuePair);
    }

    public override int GetHashCode()
    {
        var hash = new HashCode();
        hash.Add(KeyValuePair);
        return hash.ToHashCode();
    }
}

测试：

[Fact]
    public void Test1()
    {
        MyClass expectedObject = new MyClass()
        {
            KeyValuePair = new KeyValuePair<int[], string>(new int[] { 1 }, "abc")
        };
        MyClass actualObject = new MyClass()
        {
            KeyValuePair = new KeyValuePair<int[], string>(new int[] { 1 }, "abc")
        };
        Assert.Equal(expectedObject, actualObject);
    }

测试结果：

消息: Assert.Equal()失败

Answer 1

您的Equals()实现不够深入。因为：

Console.WriteLine("Are two int[] arrays equal? => "+
     EqualityComparer<int[]>.Default.Equals(new int[] { 1 }, new int[] { 1 }));

Console.WriteLine("Do two int[] have the same hashcode? => " +
     (new int[] { 1 }.GetHashCode() == new int[] { 1 }.GetHashCode()));

两个int[]数组是否相等？=> False 两个int[]有相同的哈希码吗？=> False

您还必须为Equals()数组实现int[]和GetHashCode()逻辑，例如：

public class EquatableIntArray : IEquatable<EquatableIntArray>
{
    public int[] Items { get; set; }

    public EquatableIntArray(int[] Items)
    {
        this.Items = Items;
    }

    public override bool Equals(object obj)
    {
        return Equals(obj as EquatableIntArray);
    }

    public bool Equals(EquatableIntArray other)
    {
        if (other == null) return false;
        if (ReferenceEquals(this, other)) return true;
        return other.Items != null && (this.Items?.SequenceEqual(other.Items)??false);
    }

    private int? cachedHashCode;

    public override int GetHashCode()
    {
        if (cachedHashCode.HasValue) return cachedHashCode.Value;
        int hc = Items.Length;
        for (int i = 0; i < Items.Length; ++i)
        {
            hc = unchecked(hc * 314159 + Items[i]);
        }
        return (cachedHashCode = hc).Value;
    }
}

(以上是GetHashCode()的here实现)

Console.WriteLine("Are two EquatableIntArrays equal? => " +
     EqualityComparer<EquatableIntArray>.Default.Equals(
         new EquatableIntArray(new int[] { 1 })
       , new EquatableIntArray(new int[] { 1 })));

 Console.WriteLine("Do two EquatableIntArrays have the same hashcode? => " +
      (new EquatableIntArray(new int[] { 1 }).GetHashCode()
    == new EquatableIntArray(new int[] { 1 }).GetHashCode()));

两个EquatableIntArrays相等吗？=>真 两个EquatableIntArrays有相同的哈希码吗？=>真

然后，在你的课堂上，你会看到这样的东西：

public class MyClass2 : IEquatable<MyClass2>
{
    public KeyValuePair<EquatableIntArray, string> KeyValuePair { get; set; }

    public override bool Equals(object obj)
    {
        return Equals(obj as MyClass2);
    }

    public bool Equals(MyClass2 other)
    {
        return other != null &&
               EqualityComparer<KeyValuePair<EquatableIntArray, string>>.Default.Equals(KeyValuePair, other.KeyValuePair);
    }
    private int? cachedHashCode;
    public override int GetHashCode()
    {
        if (cachedHashCode.HasValue) return cachedHashCode.Value;
        cachedHashCode = CombineHashCodes(KeyValuePair.Key.GetHashCode(), KeyValuePair.Value.GetHashCode());
        return cachedHashCode.Value;
    }

    internal static int CombineHashCodes(int h1, int h2)
    {
        return (((h1 << 5) + h1) ^ h2);
    }
}

(我在.NET Framework4.7上进行了测试，那里没有HashCode类，所以我从Tuple那里借用了GetHashCode()实现)

和：

MyClass2 expectedObject2 = new MyClass2()
{
  KeyValuePair = new KeyValuePair<EquatableIntArray, string>(new EquatableIntArray(new int[] { 1 }), "abc")
};
MyClass2 actualObject2 = new MyClass2()
{
   KeyValuePair = new KeyValuePair<EquatableIntArray, string>(new EquatableIntArray(new int[] { 1 }), "abc")
};

Console.WriteLine("Are two MyClass2 instances equal? => "+ expectedObject2.Equals(actualObject2));

两个MyClass2实例是否相等？=>真