[英]issue with EqualityComparer for KeyValuePair
我有一个KeyValuePair类,实现IEquatable之后无法按预期工作。 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
您对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 []数组相等吗? =>错误
两个int []是否具有相同的哈希码? =>错误
您还必须为int[]
数组实现Equals()
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;
}
}
(从此处实现GetHashCode()
之上)
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是否相等? =>正确
两个EquatableIntArray是否具有相同的哈希码? =>正确
然后,在您的课程中,您将获得以下内容:
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 Framework 4.7上进行了测试,并且那里没有HashCode
类,因此我从Tuple
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实例相等吗? =>正确
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