C#

class Program
{
    static void Main(string[] args)
    {
        List<Bar1> bar1List = new List<Bar1>();
        bar1List.Add(new Bar1());
        bar1List.Add(new Bar1());
        bar1List.Add(new Bar1());

        List<Bar2> bar2List = new List<Bar2>();
        bar2List.Add(new Bar2());
        bar2List.Add(new Bar2());
        bar2List.Add(new Bar2());

        List<Foo> fooList = new List<Foo>();
    }
}

abstract class Foo
{
    public string type;
    public Foo(string type)
    {
        this.type = type;
    }
}

class Bar1 : Foo
{
    public Bar1() : base("Bar1")
    {
    }
}

class Bar2 : Foo
{
    public Bar2() : base("Bar2")
    {
    }
}