Problems Implementing Generic IEnumerator and IComparable

Question

I am working on an AVL tree. The tree seems to work, but I need an iterator to go through the values ​​of the tree. So I tried to implement IEnumerator interace. Unfortunately, I get a compile-time error that implements IEnumerator and IComparable. First enter the code and below that error.

class AvlTreePreOrderEnumerator<T> : IEnumerator<T> where T :IComparable<T>
{
    private AvlTreeNode<T> current = default(T);
    private AvlTreeNode<T> tree = null;
    private Queue<AvlTreeNode<T>> traverseQueue = null;

    public AvlTreePreOrderEnumerator(AvlTreeNode<T> tree)
    {
        this.tree = tree;

        //Build queue
        traverseQueue = new Queue<AvlTreeNode<T>>();
        visitNode(this.tree.Root);
    }

    private void visitNode(AvlTreeNode<T> node)
    {
        if (node == null)
            return;
        else
        {
            traverseQueue.Enqueue(node);
            visitNode(node.LeftChild);
            visitNode(node.RightChild);
        }
    }

    public T Current
    {
        get { return current.Value; }
    }

    object IEnumerator.Current
    {
        get { return Current; }
    }

    public void Dispose()
    {
        current = null;
        tree = null;
    }

    public void Reset()
    {
        current = null;
    }

    public bool MoveNext()
    {
        if (traverseQueue.Count > 0)
            current = traverseQueue.Dequeue();
        else
            current = null;

        return (current != null);
    }
}

Error provided by VS2008: Error 1 Type "T" cannot be used as a parameter of type "T" in the generic type or method "Opdr2_AvlTreeTest_Final.AvlTreeNode". There is no conversion of box conversion or conversion of type parameters from "T" to "System.IComparable".

This error is indicated on the following lines:

    //members
    private AvlTreeNode<T> current = default(T);  //current highlighted
    private AvlTreeNode<T> tree = null;   //tree highlighted
    private Queue<AvlTreeNode<T>> traverseQueue = null;   //traverseQueue highlighted  

    //Constructor
    public AvlTreePreOrderEnumerator(AvlTreeNode<T> tree)  // AvlTreePreOrderEnumerator highlighted  
    //Method
    private void visitNode(AvlTreeNode<T> node)   //visitNode highlighted  

node. , , !

!

Answer 1

class AvlTreePreOrderEnumerator<T> : IEnumerator<T> where T :IComparable

Answer 2

, node :

public class AvlTreeNode<T> where T : IComparable<AvlTreeNode<T>> {
    public AvlTreeNode<T> Root;
    public AvlTreeNode<T> LeftChild {get;set;}
    public AvlTreeNode<T> RightChild {get;set;}
    public T Value { get; set;}
}

( IComparable):

public class AvlTreeNode<T> where T : IComparable<T> {
    public AvlTreeNode<T> Root;
    public AvlTreeNode<T> LeftChild {get;set;}
    public AvlTreeNode<T> RightChild {get;set;}
    public T Value { get; set;}
}

current :

private AvlTreeNode<T> current = new AvlTreeNode<T>();

Answer 3

, (Opdr2_AvlTreeTest_Final.AvlTreeNode), , , / , IComparable<T>.

:

// no problem here at definition site:
void IsLarger<T>(T a, T b) where T : IComparable<T> {
   return a.CompareTo(b) > 0;
}

void Test<T>(T arg) { // note: T is not necessarily IComparable<T>
   Console.WriteLine(IsLarger(arg, arg)); // The compiler shouldn't allow this.
}

Answer 4

As already mentioned, you did not include all the code, but you only limited T to IComparable <T>, while the error you indicated is that he wants T to implement IComparable (i.e. not a generic form from IComparable)