为什么我必须定义IEnumerator <T> .Current＆IEnumerator.Current，它实现了什么？

Question

When implementing IEnumerable & IEnumerator on a class I was writing during training, I noticed that I was required to specify two implementations for the property "Current".

public class PeopleEnumerator : IEnumerator<Person>
{
    People people; // my collection I'm enumerating (just a wrapped array).
    int index; // my index to keep track of where in the collection I am.

    ...

    //implementation for Person
    public Person Current { get { return people[index]; } }

    //implementation for object
    object Enumerator.Current { get { return people[index]; } }
}

I roughly understand that I'm implementing some non-generic version of IEnumerator and a "Current" property for it, however I don't understand the following things:

• Why am I allowed to overload by return type here? Presumably it has something to do with the explicit IEnumerator.Current; however the reasons are opaque to me.
• Why can "object IEnumerator.Current" not be specified as "public"?

Thanks in advance!

Answer 1

There's only one reason you must implement two different interfaces: backwards compatibility. C# 1.0 did not have generics.
In C# 2.0, we got IEnumerator<T> which extends the 1.0 IEnumerator .

• Why am I allowed to overload by return type here? Presumably it has something to do with the explicit IEnumerator.Current; however the reasons are opaque to me.

You cannot overload methods or properties by return type only; that's why one of them must be an explicit implementation.

• Why can "object IEnumerator.Current" not be specified as "public"?

Same reason. It has to be an explicit implementation. An explicit implementation cannot have a visibility modifier as a rule. It cannot possibly have any other visibility. IEnumerator.Current can only be called through an instance of the IEnumerator interface.