为什么检查开放泛型类型的相等性不一致？ [复制]

Question

出于某种原因：

typeof(Dictionary<string,string>).GetGenericTypeDefinition()
                                 .GetInterfaces()
                                 .Contains(typeof(IDictionary<,>))

是false 但是这个：

typeof(Dictionary<string,string>).GetInterfaces()
                                 .Any(i => i.IsGenericType
                                        && i.GetGenericTypeDefinition() == typeof(IDictionary<,>))

是 true，即使它们在调试器中都显示为 IDictionary'2，具有相同的 GUID。

在第一个示例中，接口数组中的[0] 是IDictionary'2，如果我直接将它与typeof（没有.Contains(...)）与== 或.Equals(...) 甚至.IsAssignableFrom(...) 进行比较结果是一样的。

请有人告诉我为什么！

Answer 1

因为从.GetGenericTypeDefinition().GetInterfaces() 返回的接口不是“泛型类型定义”（它们的IsGenericTypeDefinition 是false），所以它们不能严格等于IDictionary<,>（即泛型类型定义， IsGenericTypeDefinition 即 true)。

第二段代码从接口深入到它们的泛型类型定义，让您进行比较。

一个简单的例子：

class MyDictionary<TKey2, TValue2> : IDictionary<TKey2, TValue2>
{
    public TValue2 this[TKey2 key] { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    public ICollection<TKey2> Keys => throw new NotImplementedException();
    public ICollection<TValue2> Values => throw new NotImplementedException();
    public int Count => throw new NotImplementedException();
    public bool IsReadOnly => throw new NotImplementedException();
    public void Add(TKey2 key, TValue2 value) => throw new NotImplementedException();
    public void Add(KeyValuePair<TKey2, TValue2> item) => throw new NotImplementedException();
    public void Clear() => throw new NotImplementedException();
    public bool Contains(KeyValuePair<TKey2, TValue2> item) => throw new NotImplementedException();
    public bool ContainsKey(TKey2 key) => throw new NotImplementedException();
    public void CopyTo(KeyValuePair<TKey2, TValue2>[] array, int arrayIndex) => throw new NotImplementedException();
    public IEnumerator<KeyValuePair<TKey2, TValue2>> GetEnumerator() => throw new NotImplementedException();
    public bool Remove(TKey2 key) => throw new NotImplementedException();
    public bool Remove(KeyValuePair<TKey2, TValue2> item) => throw new NotImplementedException();
    public bool TryGetValue(TKey2 key, out TValue2 value) => throw new NotImplementedException();
    IEnumerator IEnumerable.GetEnumerator() => throw new NotImplementedException();
}

然后：

var interfaces = typeof(MyDictionary<string, string>).GetGenericTypeDefinition().GetInterfaces();
var idict1 = interfaces[0];
var idict2 = idict1.GetGenericTypeDefinition();

Console.WriteLine(idict1);
Console.WriteLine(idict2);

结果：

System.Collections.Generic.IDictionary`2[TKey2,TValue2] <-- This is what you get with GetInterfaces()
System.Collections.Generic.IDictionary`2[TKey,TValue]   <-- And this is the generic type definition

很明显idict1不可能是IDictionary<,>，因为它是IDictionary<TKey2, TValue2>