Cast/Convert IEnumerable to IEnumerable?

Answer 1

You can't just cast two unrelated type into each other. You could make it possible to convert PersonWithAge to Person by letting PersonWithAge inherit from Person. Since PersonWithAge is obviously a special case of a Person, this makes plenty of sense:

class Person
{
        public int Id { get; set; }
        public string Name { get; set; }
}

class PersonWithAge : Person
{
        // Id and Name are inherited from Person

        public int Age { get; set; }
}

Now if you have an IEnumerable named personsWithAge, then personsWithAge.Cast() will work.

In VS 2010 you will even be able to skip the cast altogether and do (IEnumerable)personsWithAge, since IEnumerable is covariant in .NET 4.