Make IImmutableList covariant like IReadOnlyList, IEnumerable etc.

[ghost]

I need System.Collections.Immutable interfaces such as IImmutableList to be covariant just like IReadOnlyList, IEnumerable in order to be able to write stuff like this:

public interface IResources<out T> where T : IDomainEntity
{
        IImmutableList<T> ShouldWorkButCompilerGivesErrorDueToIImmutableListNotCovariant { get; }
        IReadOnlyList<T> Works { get; }
}

[vcsjones]

I don't think it can reasonably be made covariant since the interface has contravariant methods
like Add<T>

[ghost]

Maybe it can be done if the covariant methods are moved to a new interface like IImmutableListBase that IImmutableList inherits from ?

[CodesInChaos]

@bluemmc Almost all covariant methods are already on IReadOnlyList<T>. So it sounds like you want is some kind of marker that tells you that this collection is immutable without adding any functionality on top of IReadOnlyList<T>.

[vcsjones]

IImmutableList<T> already implements the IReadOnlyList<T> interface, which is pretty much the interface you're asking for.

[ghost]

Thanks for all the feedback. You are both right. I will have to do with IReadOnlyList when I need it in covariant form (as I do in my example).