If I cast an IQueryable as an IEnumerable then call a Linq extension method, which implementation gets called?

Question

Considering the following code:

IQueryable<T> queryable;

// something to instantiate queryable

var enumerable = (IEnumerable<T>) queryable;

var filtered = enumerable.Where(i => i > 3);

In the final line, which extension method gets called?

Is it IEnumerable<T>.Where(...)? Or will IQueryable<T>.Where(...) be called because the actual implementation is still obviously a queryable?

Presumably the ideal would be for the IQueryable version to be called, in the same way that normal polymorphism will always use the more specific override.

In Visual Studio though when I right-click on the Where method and "Go to Definition" I'm taken to the IEnumerable version, which kind of makes sense from a visual point-of-view.

My main concern is that if somewhere in my app I use Linq to NHibernate to get a Queryable, but I pass it around using an interface that uses the more general IEnumerable signature, I'll lose the wonders of deferred database execution!

---

Edit: It turns out that, as Iridium has pointed out, it's the Enumerable version that gets called

public class Program
    {
        static void Main(string[] args)
        {
            var myString2 = new MyString2();
            var myString = (MyString)myString2;
            Console.WriteLine(myString.Method());
            Console.ReadLine();
        }
    }

    public class MyString {}

    public class MyString2 : MyString {}

    public static class ExtensionMethods
    {
        public static string Method(this MyString instance)
        {
            return "MyString method";
        }

        public static string Method(this MyString2 instance)
        {
            return "MyString2 method";
        }
    }

The output is "MyString method".

Answer 1

The currently accepted answer deals with virtual methods, not extension methods.

If you cast an IQueryable to an IEnumerable and then call one of the extension methods (e.g. Where(...) in your question), then the one on Enumerable version will be called, not the Queryable one.