Generics challenge!

[tm123456789]

Are you confident that you fully understand Generics?

Here's a challenge to see if you do.

Below is a simple test app that creates an array of a generic type and attempts to sort it. The generic class definition is incomplete (look for the ???). Can you fill in the missing parts and avoid the error "failed to compare two elements in the array" - or indeed some other error?

(By the way, the only reason I'm posting this challenge is that this problem stumped me initially and I thought it would be good to have it documented somewhere on the internet in case others encounter similar problems).

 
using System;
 
class Program
{
    static void Main(string[] args)
    {
        Program.Test();
    }
 
    static void Test()
    {
        try
        {
            // Create an array of a generic type - MyClass<T> 
            // Strongly type it to double.
            // add three elements to the array.
            MyClass<Double>[] arr = new MyClass<Double>[] 
                { 
                    new MyClass<Double>(334.6678967), 
                    new MyClass<Double>(54534.6), 
                    new MyClass<Double>(145.4) 
                };
 
            // View the values unsorted 
            Console.WriteLine("Unsorted\n-------------");
            foreach (MyClass<Double> var in arr)
            {
                Console.WriteLine(var.ToString());
            }
 
            // Sort the array
            Array.Sort<MyClass<Double>>(arr);
 
            // View the sorted values 
            Console.WriteLine("\nSorted\n-------------");
            foreach (MyClass<Double> var in arr)
            {
                Console.WriteLine(var.ToString());
            }
 
            Console.WriteLine("\n");
 
        }
        catch (InvalidOperationException ioe)
        {
            Console.Write("\nUnlucky, try again.\n\n" 
                     + ioe.ToString());
        }
 
    }
 
}
 
public class MyClass<T> // ??? complete the class definition here 
                      // to make the code compile and run.
{
    private T _data;
 
    public MyClass(T data)
    { _data = data; }
 
    public int CompareTo( /*  ??? complete the definition here */)
    { return _data.CompareTo(other._data); }
 
    public override string ToString()
    { return _data.ToString(); }
}
 
 
 

Good luck.
T

p.s. I'll post the solution soon if no one else does.

[tm123456789]

Here is what the completed MyClass definition should be:

public class MyClass<T> : IComparable<MyClass<T>> 
    where T : IComparable<T> 
{
    private T _data;
 
    public MyClass(T data)
    { _data = data; }
 
    public int CompareTo(MyClass<T> other)
    { return _data.CompareTo(other._data); }
 
    public override string ToString()
    { return _data.ToString(); }
}
 

Note that MyClass must implement IComparable<MyClass<T>> in order to be able to compare two instances of itself (CompareTo is called internally by the CLR when sorting the array). Also, because the CompareTo method of an object of type T is actaully being called, T must also be constrained to implement IComparable<T> - otherwise the CompareTo method being called by _data would not be available.