Cast/Convert IEnumerable to IEnumerable?

Answer 1

You can keep the IEnumerable and don't convert it to IEnumerable. Just add an implicit conversion to convert an object of PersonWithAge to Person when you need.

class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public static implicit operator Person(PersonWithAge p)
    {
        return new Person() { Id = p.Id, Name = p.Name };
    }
}

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List pwa = new List
Person p = pwa[0];