Is there a way to say an IList<xxx> is both a specific class and an interface

Question

I would like to declare a property as:

IList<BaseNode and IComplexType> ComplexTypes { get; }

All elements in the list inherit from BaseNode and implement IComplexType. Is there any way to do this? It won't work to create a class BaseNodeComplexType because the nodes in the list are all sub-classes of BaseNode.

Update: I didn't think this through to explain fully. I have sub classes such as XmlNode. XmlNode inherits from BaseNode. I also have XmlComplexNode that inherits from XmlNode and implements IComplexType. But XmlNode does not inherit from IComplexType (and I don't want it to as I use "obj is IComplexType" in places. apologies for not adding this originally.

Answer 1

No, but you could solve it with generics?

class CustomObj<T> where T : BaseNode, IComplexType
{
   IList<T> ComplexTypes { get; }
}

For more details about the used generic-constraints, see this page.

Answer 2

The correct behaviour would be to derive a new class i.e. ComplexBaseNode which has both the inherited features of BaseNode and interface IComplexType, would it not?

Answer 3

There's no direct way to do that.

But you can use generics to achieve that: what about a generic type parameter?

public class YourClass<T> 
  where T : BaseNode, IComplexType

... and your property will look like this:

IList<T> ComplexTypes { get; }

Answer 4

Where's your IList<> residing. If you use a generic parameter xxx (from your title), you can say where xxx : BaseNode, IComplexType.

Also consider if BaseNode could already implement IComplexType, possibly abstractly.

Answer 5

The definition of IList<T> means that you can only specify one type for the elements in the list.

Create a container class: ComplexNodeContainer<T,U>, that will contain BaseNode objects implementing also IComplexType, when T=BaseNode and U=IComplexType.

When you set the "contained" object(in the constructor preferably, or via a method/property), you can check whether it implements both types or not, and act accordingly.

You can have two properties to retrieve it, one as type T (or BaseNode), one as type U (or IComplexType in this case).

Then you can define your property as: IList<ComplexNodeContainer>