为什么通用 ICollection 不在 .NET 4.5 中实现 IReadOnlyCollection?

问题描述

在 .NET 4.5/C# 5 中，IReadOnlyCollection 使用 Count 属性声明:

公共接口 IReadOnlyCollection;: IEnumerable, IEnumerable{int计数{得到；}}

我想知道，ICollection 也实现 IReadOnlyCollection 接口是否有意义:

公共接口ICollection: IEnumerable, IEnumerable, *IReadOnlyCollection*

这意味着实现 ICollection 的类会自动实现 IReadOnlyCollection.这对我来说听起来很合理.

ICollection 抽象可以看作是 IReadOnlyCollection 抽象的扩展.请注意，例如，List 实现了 ICollection 和 IReadOnlyCollection.

然而，它并不是这样设计的.

我在这里错过了什么?为什么会选择当前的实现?

更新

我正在寻找使用面向对象设计推理来解释原因的答案:

• 一个具体的类，例如 List 实现 IReadOnlyCollection 和 ICollection>

比以下更好的设计:

• ICollection 直接实现IReadOnlyCollection

另请注意，这与以下问题基本相同:

1. 为什么IList没有实现IReadOnlyList?
2. 为什么IDictionary没有实现IReadOnlyDictionary?

解决方案

Jon 就在这里 https://stackoverflow.com/a/12622784/395144 ，你应该把他的回复标记为答案:

int ICollection.Count { ... }//编译器错误！

由于接口可以有显式实现，提取基接口不向后兼容(使用基类你没有这个问题).

这就是为什么...

集合: IReadOnlyCollection列表: IReadOnlyList字典: IReadOnlyDictionary

...但不是他们的接口.

恕我直言，他们最初犯了一个设计错误，现在无法解决(不会破坏事物).

隐藏没有帮助，旧的(显式)实现仍然不会构建(不修改代码):

interface INew{ T 获取()；}接口IOld <T>:INew<T>{无效集(T值)；新 T 获取()；}老式<T>:IOld T{T IOld.Get() { 返回默认值(T);}void IOld.Set(T value) { }}

'Sample.Old' 没有实现接口成员 'Sample.INew.Get()'

In .NET 4.5 / C# 5, IReadOnlyCollection<T> is declared with a Count property:

public interface IReadOnlyCollection<out T> : IEnumerable<T>, IEnumerable
{
    int Count { get; }
}

I am wondering, wouldn't it have made sense for ICollection<T> to implement the IReadOnlyCollection<T> interface as well:

public interface ICollection<T> : IEnumerable<T>, IEnumerable, *IReadOnlyCollection<T>*

This would've meant that classes implementing ICollection<T> would've automatically implemented IReadOnlyCollection<T>. This sounds reasonable to me.

The ICollection<T> abstraction can be viewed as an extension of the IReadOnlyCollection<T> abstraction. Note that List<T>, for example, implements both ICollection<T> and IReadOnlyCollection<T>.

However it has not been designed that way.

What am I missing here? Why would the current implementation have been chosen instead?

---

UPDATE

I'm looking for an answer that uses Object Oriented design reasoning to explain why:

• A concrete class such as List<T> implementing both IReadOnlyCollection<T> and ICollection<T>

is a better design than:

• ICollection<T> implementing IReadOnlyCollection<T> directly

---

Also please note that this is essentially the same question as:

1. Why doesn't IList<T> implement IReadOnlyList<T>?
2. Why doesn't IDictionary<T> implement IReadOnlyDictionary<T>?

解决方案

Jon was right here https://stackoverflow.com/a/12622784/395144 , you should mark his reply as the answer:

int ICollection<Foo>.Count { ... } // compiler error!

Since interfaces can have explicit implementations, extracting base interfaces is not backward compatible (with base classes you don't have this problem).

That's why...

Collection<T> : IReadOnlyCollection<T>
List<T> : IReadOnlyList<T>
Dictionary<TKey, TValue> : IReadOnlyDictionary<TKey, TValue>

... but not their interfaces.

IMHO, they did a design error initially, quite unresolvable now (without breaking things).

EDIT: hiding doesn't help, old (explicit) implementations won't still build (without modifying the code):

interface INew<out T> { T Get(); }

interface IOld<T> : INew<T>
{
    void Set(T value);
    new T Get();
}

class Old<T> : IOld<T>
{
    T IOld<T>.Get() { return default(T); }
    void IOld<T>.Set(T value) { }
}

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