Can I force an implementing class to return an object of its own type?

Question

I want to make an interface in C# that defines a method that always returns an object of the implementing class, thus:

public interface IParser {
    IParser Parse(string s);
}

public class Parser : IParser {
    public Parser Parse(string s) {
        return new Parser(s);
    }
}

Can I force an implementing class to return an object of its own type? If possible, then how? Or is generics the answer here?

NB: The code is just an illustration, not something that's supposed to run.

Answer 1

Generics is the answer here.

public interface IParser<T> where T:IParser<T> {
    T Parse(string s);
}

public class Parser : IParser<Parser> {
    public Parser Parse(string s) {
        return new Parser(s);
    }
}

Answer 2

Not in the interface declaration, no. The best you could manage is with generics:

public interface IParser<T>
    where T: IParser<T>
{
    T Parse(string s);
}

public class Parser
 : IParser<Parser>
{
    public Parser Parse(string s)
    {
       return new Parser(s);
    }
}

This doesn't force the implementation to return it's own type, but at least it allows it to do so. This is why the IClonable interface returns an object from its Clone method, rather than a specific type.

----Edit----

Something to remember on this question: let's say that my code, for which you don't have any knowledge of the implementation, returns an IParser, and your code calls the Parse method. What object do you expect to be returned, not knowing the concrete type of returned IParser reference? I think you're trying to use interfaces for something they're not meant to do...