[英]Custom equality comparer for Type in dictionary
Since Int32
is a Object
, I want this to print "True"由于Int32
是一个Object
,我希望它打印“True”
Dictionary<Type, string> dict = new Dictionary<Type, string>(new MyComparer());
dict[typeof(object)] = "Hello";
Console.WriteLine(dict.ContainsKey(typeof(int))); // currently prints false :(
Here's the comparer I tried:这是我尝试过的比较器:
public class MyComparer : IEqualityComparer<Type>
{
public bool Equals(Type x, Type y)
{
return y.IsAssignableFrom(x);
}
public int GetHashCode(Type obj)
{
return obj.GetHashCode();
}
}
But it's not working.但它不起作用。 I'm not quite sure what to return in GetHashCode
- I know it's wrong cause when debugging I'm not even reaching Equals
- Any idea how to write this correctly?我不太确定在GetHashCode
返回什么 - 我知道调试时这是错误的原因我什至没有达到Equals
- 知道如何正确编写它吗? Thanks.谢谢。
That simply is not a valid comparer for a dictionary, and the result is not well-defined.这根本不是字典的有效比较器,结果也没有明确定义。 Equality comparisons should be commutative, specifically a eq b
if and only if b eq a
.相等比较应该是可交换的,特别a eq b
当且仅当b eq a
。 That does not apply in your case.这不适用于您的情况。 Likewise, a valid hash-code implementation states that:同样,有效的哈希码实现声明:
That fails too.那也失败了。
Basically, that isn't going to work.基本上,这是行不通的。
Specifically,from MSDN :具体来说,来自 MSDN :
Notes to Implementers给实施者的注意事项
Implementations are required to ensure that if the Equals method returns true for two objects x and y, then the value returned by the GetHashCode method for x must equal the value returned for y.实现需要确保如果 Equals 方法对两个对象 x 和 y 返回true ,则 GetHashCode 方法为 x 返回的值必须等于为 y 返回的值。
The Equals method is reflexive, symmetric, and transitive. Equals 方法是自反的、对称的和可传递的。 That is, it returns true if used to compare an object with itself;也就是说,如果用于将对象与自身进行比较,则返回true ; true for two objects x and y if it is true for y and x;真两个对象的x和y,如果它是用于y和x真; and true for two objects x and z if it is true for x and y and also true for y and z.和真正的两个对象x和z如果是Y和Z x和y的真实,也是如此。
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