C#

public class Cmp
{
  public string Name { get; set; }
}

public class Cmp : IComparable<Cmp>
{
  public string Name { get; set; }
  public int CompareTo(Cmp obj)
  {
    if (Name == null) return -1;
    return Name.CompareTo(obj.Name);
  }
}

public class CustomCmpComparer : IComparer<Cmp>
{
  public int Compare(Cmp x, Cmp y)
  {
    if (x.Name == null) return -1;
    return x.Name.CompareTo(y.Name);
  }
}

myList.Sort(new CustomCmpComparer());

public interface IMyInterface
{
    bool Compare(object target);
}

public class MyClass : IMyInterface
{
    public bool Compare(object target)
    {
        // implement this method properly
        return true;
    }
}

private void MyFunction<T>(T data, T data2) where T : IMyInterface
{
    data.Compare(data2);
}

MyFunction<MyClass>(new MyClass(), new MyClass()); // valid
MyFunction<SqlConnection>(new SqlConnection(), new SqlConnection()); // not valid as SqlConnection does not implement IMyInterface