Question

i have a question regarding the visitor pattern, I currently have two assemblies. My first assembly contains several interfaces.

public interface INode {     void Visit(INodeVisitor visitor); }  public interface INodeVisitor {     void VisitContainer(IContainer container); }  public interface IContainer : INode { } 

And my second assembly

    class Program {     static void Main(string[] args)     {         ContainerVisitor visitor = new ContainerVisitor();         visitor.VisitContainer(new Container());     } }  public class ContainerVisitor : INodeVisitor {     public void VisitContainer(IContainer value)     {         Container container = value as Container;         // Do some stuff...     } }  public class Container : IContainer {             public void Visit(INodeVisitor visitor)     {         visitor.VisitContainer(this);     } } 

What i want to do is avoid the need to cast in the ContainerVisitor class, I want to reference the Container directly. I cannot change the interface INodeVisitor interface to use Container. Any ideas? Should i just cast?

Cheers

Rohan

Answer 1

The cast is unavoidable, but you could abstract it out a bit to remove it from the actual ContainerVisitor class.

public class NodeVisitor<T> : INodeVisitor where T : IContainer {   public void VisitContainer(T node) {     var container = node as T;     if ( container != null ) {        VisitTyped(container);     }   }   protected abstract VisitContainerTyped(T container); } 

Now ContainerVisitor can derive from NodeVisitor and avoid the cast

public class ContainerVisitor : NodeVisitor<Container>{     protected override void VisitContainerTyped(Container container){         // Do some stuff...     } }