为什么 HashSet&lt;T&gt;没有实现 IReadOnlyCollection<T>? [英] Why HashSet&lt;T&gt; does not implement IReadOnlyCollection&lt;T&gt;?

问题描述

我刚刚发现 .NET Fx 现在有 3 个有用的接口:

1. IReadOnlyCollection
2. IReadOnlyList
3. IReadOnlyDictionary

我有点困惑为什么 HashSet<T> 没有实现 IReadOnlyCollection?是不是有什么原因，还是微软又忘记设置了?

UPD

经过两个小时的谷歌搜索，我发现 BCL 中有许多集合具有 .Count 属性但没有实现 IReadOnlyCollection 接口.>

UPD2

我找到了这篇文章 http://social.msdn.microsoft.com/Forums/en/netfxbcl/thread/b4fb991a-3f5c-4923-93d4-7cd5c004f859 和 Immo Landwerth 的回答，他在哪里下面说

<块引用>

除了 List<> 和 Dictionary<> 之外的其他集合是否会更新为支持这些接口吗?

绝对的.事实上，我们所有的内置集合类型已经实现 IReadOnlyList<> 和 IReadOnlyDictionary<>.这意味着，你可以直接将 List、T[] 或 Dictionary<> 的实例传递给一个需要 IReadOnly 版本的 API.

解决方案

在 4.5 版框架中，HashSet 没有实现 IReadOnlyCollection.

这个遗漏在框架的 4.6 版中得到解决(在提出上述问题后近 12 个月发布).

这些更正是不限于HashSet，其他集合如Stack<;T> 和 队列; 已收到这些改进.

对任何遗漏原因的猜测没有实际意义.这可能是疏忽或时间压力，但坦率地说，这无关紧要.我怀疑即使来自 Microsoft 开发团队的直接输入也会有些主观，即使我们喜欢相关的轶事.

I've just found that .NET Fx now has 3 useful interfaces:

1. IReadOnlyCollection<T>
2. IReadOnlyList<T>
3. IReadOnlyDictionary<K,V>

And I'm bit confused why HashSet<T> do not implement IReadOnlyCollection<T>? Are there any reasons, or Microsoft just forgot about sets again?

UPD

After two-hours googling I've found that there are many collections in BCL which has .Count property but do not implement IReadOnlyCollection<T> interface.

UPD2

I've found this post http://social.msdn.microsoft.com/Forums/en/netfxbcl/thread/b4fb991a-3f5c-4923-93d4-7cd5c004f859 and the answer by Immo Landwerth where he've said following

Will other collections besides List<> and Dictionary<> be updated to support these interfaces?

Absolutely. In fact, all of our built-in collection types already implement IReadOnlyList<> and IReadOnlyDictionary<>. This means, you can directly pass an instance of List, T[] or Dictionary<> to an API that takes an IReadOnly-version of it.

解决方案

In version 4.5 of the framework, HashSet<T> does not implement IReadOnlyCollection<out T>.

This omission was resolved in version 4.6 of the framework (released almost 12 months after the above question was asked).

These corrections are not limited to HashSet<T>, other collections such as Stack<T> and Queue<T> have received these improvements.

Speculation on the reason for any omission is moot. It may be oversight or time pressure but frankly, it is of little consequence. I suspect that even direct input from the Microsoft Development Team would be somewhat subjective, even if we enjoy associated anecdotes.

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