c# - IReadOnlyDictionary 缺乏协方差

Question

我已阅读相关问题（How to get around lack of covariance with IReadOnlyDictionary?），但我不明白它如何帮助解决我的问题。

这是Box可以编辑（使用IBoxTarget）并通知更改（使用IBoxSource）的内容：

interface IBoxTarget
{
    void DoSomething();
}

interface IBoxSource
{
    event Action SomethingIsDone;
}

class Box : IBoxTarget, IBoxSource
{
    public void DoSomething()
    {
        // . . . some logic . . .

        if (SomethingIsDone != null) SomethingIsDone();
    }

    public event Action SomethingIsDone;
}

Room是一个容器Box。它还实现了两个接口：

interface IRoomTarget
{
    IReadOnlyDictionary<string, IBoxTarget> Boxes { get; }
}

interface IRoomSource
{
    IReadOnlyDictionary<string, IBoxSource> Boxes { get; }
}

class Room : IRoomTarget, IRoomSource
{
    Dictionary<string, Box> boxes = new Dictionary<string, Box>();

    IReadOnlyDictionary<string, IBoxTarget> IRoomTarget.Boxes
    {
        get { return boxes; } // Error: "Cannot implicitly convert type ..."
    }

    IReadOnlyDictionary<string, IBoxSource> IRoomSource.Boxes
    {
        get { return boxes; } // Error: "Cannot implicitly convert type ..."
    }
}

我不想在里面创建两个不同的字典Room。我需要做什么？

Answer 1

在我的特殊情况下，这有帮助：

interface IRoomTarget
{
    IBoxTarget this[string name] { get; }
}

interface IRoomSource
{
    IBoxSource this[string name] { get; }
}

class Room : IRoomTarget, IRoomSource
{
    Dictionary<string, Box> boxes = new Dictionary<string, Box>();

    public IBoxTarget IRoomTarget.this[string name]
    {
        get { return boxes[name]; }
    }

    IBoxSource IRoomSource.this[string name]
    {
        get { return boxes[name]; }
    }
}

但我不确定这是通用解决方案