[tigershark]

This tells me that you never really looked at functional languages, not even used them. The power of ADT, especially when using a comprehensive pattern matching expression, is pretty difficult to emulate in the OOP world without a ton of code. But in this extremely simple case you just need a record.

    let dogBar = {Name = “bar”; Age = 11; Friends = []}
    let dogFoo = {Name = “foo”; Age = 12; Friends = [dogBar]}
    printfn “%A” dogFoo.Friends 

The advantage is that it’s immutable and it’s guaranteed to don’t have null in any fields. C# only introduced records recently, while F# was born with them. And C# still hasn’t got ADT because it’s missing the Union types as far as I remember.