Question

I can’t seem to find out how to do this in .NET2.0 despite searching Google and SO.

Say I have the following classes:

public class Fruit {
    prop string Color {get; set;}
}

public class Apple : Fruit {
    public Apple() {
        this.Color = "Red";
    }
}

public class Grape: Fruit {
    public Grape() {
        this.Color = "Green";
    }
}

Now I want to do this:

public List<Fruit> GetFruit() {
    List<Fruit> list = new List<Fruit>();
    // .. populate list ..
    return list;
}    


List<Grape> grapes = GetFruit();

But of course I get Cannot implicitly convert type Fruit to Grape.

I realize this is because I could really mess things up if I did:

List<Grape> list = new List<Grape>();
list.add(new Apple());

Because while both are Fruit, an Apple isn’t a Grape. So that makes sense.

But I don’t understand why I can’t do this:

List<Fruit> list = new List<Fruit>();
list.add(new Apple());
list.add(new Grape());

At the very least, I need to be able to:

List<Fruit> list = new List<Fruit>();
list.add(new Apple());   // will always be Apple
list.add(new Apple());   // will always be Apple
list.add(new Apple());   // will always be Apple

Any ideas on how to do this in .NET2?

Thanks

EDIT

Sorry, I was mistaken. I can in fact do:

List<Fruit> list = new List<Fruit>();
list.add(new Apple());
list.add(new Grape());

The .FindAll and .Convert did the trick.

Answer 1

Since you need something specific in .Net 2.0 first I would filter each using FindAll then use ConvertAll.

List<Grape> grapes = list
  .FindAll(delegate(Fruit f) { return f is Grape; })
  .ConvertAll<Grape>(delegate(Fruit f) { return f as Grape; });

As for your questions:

But I don’t understand why I can’t do this:

List<Fruit> list = new List<Fruit>();
list.Add(new Apple());
list.Add(new Grape());

You can do this, it is completely valid, did you mistype something (add vs Add)?