Abstract base class within abstract base class

Question

I have a an abstract base class FooBase that's inherited by Foo. And I have another abstract base class BarBase that's inherited by Bar. BarBase contains an abstract FooBase property. And in Bar I want to set the FooBase property to Foo. Why is this not allowed? Is this a crazy design that needs to be rethought, or can it be done in some way?

public abstract class FooBase
{
}

public class Foo : FooBase
{
}

public abstract class BarBase
{
    public abstract FooBase Foo { get; set; }
}

public class Bar : BarBase
{
    public override Foo Foo { get; set; }
}

Use generics, just like Patrick's answer demonstrates – maccettura Feb 01 '18 at 14:43 — maccettura, Feb 01 '18 at 14:43

score 1 · Accepted Answer · answered Feb 01 '18 at 14:42

Because you can't change the signature when overriding. Period. That is how C# was designed. A better solution here would be using generics:

public abstract class FooBase
{
}

public class Foo : FooBase
{
}

public abstract class BarBase<F> where F : FooBase
{
    public F Foo { get; set; }
}

public class Bar : BarBase<Foo>
{
}

Abstract base class within abstract base class

1 Answers1