C#•3y ago

✅ How do I deal with generic covariance and collections types?

Let's say I have osmething like the following:

public interface IBoxCollection<out T> : IBox
    where T : IBox
{
    public Dictionary<string, T> Collection { get; }
}

public interface IBoxCollection<out T> : IBox
    where T : IBox
{
    public Dictionary<string, T> Collection { get; }
}

public interface IBoxCollection<out T> : IBox
    where T : IBox
{
    public Dictionary<string, T> Collection { get; }
}

public interface IBoxCollection<out T> : IBox
    where T : IBox
{
    public Dictionary<string, T> Collection { get; }
}

I get the following error:

Invalid variance: The type parameter 'T' must be invariantly valid on 'IBoxCollection<T>.Collection'. 'T' is covariant

Invalid variance: The type parameter 'T' must be invariantly valid on 'IBoxCollection<T>.Collection'. 'T' is covariant

Invalid variance: The type parameter 'T' must be invariantly valid on 'IBoxCollection<T>.Collection'. 'T' is covariant

Invalid variance: The type parameter 'T' must be invariantly valid on 'IBoxCollection<T>.Collection'. 'T' is covariant

I've looked around on how to resolve this issue but haven't found anything. Is there an easy solution to this problem, or is there a pattern which will accomplish what I'm looking for?

✅ How do I deal with generic covariance and collections types?

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