C# Generic Class Types and IComparable, cannot compare type T

Question

I am trying to implement a Binary Search Tree in C# using generics, but I have no idea how to implement the IComparable interface. I cannot compare generic type T so I don't know how to implement CompareTo() function.

Here is the code:

public class BSTNode<T> : IComparable<BSTNode<T>>
{
    public T Data { get; set; }
    public BSTNode<T> LeftChild { get; private set; }
    public BSTNode<T> RightChild { get; private set; }

    ...
}

When trying to implement public void Insert(BSTNode<T> node) , I need to compare Data property, but I get an error saying I cannot compare generic types T.

I tried to implement the IComparable interface but in the CompareTo function, it's the same you cannot compare to T error. Any ideas how I can fix this?

Answer 1

If you add a constraint to your generic type, that will work.

public class BSTNode<T> : IComparable<BSTNode<T>> where T : IComparable<T>
{
    public T Data { get; set; }
    public BSTNode<T> LeftChild { get; private set; }
    public BSTNode<T> RightChild { get; private set; }

    public int CompareTo(BSTNode<T> other)
    {
        return this.Data.CompareTo(other.Data);
    }
}

Answer 2

What you need is a generic type constraint:

public class BSTNode<T> : IComparable<BSTNode<T>>
    where T : IComparable<T>

That will let you call CompareTo on Data .