C# Generics: What does IComparable<Nullable<T>> mean?

Question

In the following chunk of code:

public struct Nullable<T> : IFormattable, IComparable, INullable,
       IComparable<Nullable<T>>
{
       // ...
}

I understand that this struct is implementing these interfaces but I do not get the IComparable<Nullable<T>> part. What it means?

Answer 1

It means that you can compare any Nullable<T> with another instance of Nullable<T> (for the same T ) in a strongly typed way. It will have a method like this:

public int CompareTo(Nullable<T> other)

Note that the normal Nullable<T> struct doesn't have any of these interfaces. Personally I think it would be somewhat confusing to have another Nullable<T> struct kicking around the place... I would suggest that if it's in your power to do so, you rename this struct to something else. It's also pretty strange that T isn't constrained using the where T: struct constraint...