- Paul Graham on Disconnected Distraction

- David Heinemeier Hansson on starting small

public struct Tuple < TFirst,TSecond >
{
    public TFirst first;
    public TSecond second;

    public Tuple(TFirst first, TSecond second)
   {
	this.first = first;
	this.second = second;
   }
}

[...]

Tuple < int,string > t = new Tuple < int,string >(1, "1");
Tuple < int,string > t2 = new Tuple < int,string >(2, "2");

List < tuple < int,string > > lt = new List < tuple < int,string > >();
lt.Add(t);
lt.Add(t2);

List < tuple < int,string > > lt2 = new List < tuple < int,string > >();
lt2.Add(t);
lt2.Add(t2);

System.Console.WriteLine("eq {0}, == {1}", lt.Equals(lt2), lt == lt2);

Which gives the following result:

eq False, == False

Ok that was strange, in Python and C++ one doesn’t have to use Equal or anything similar and furthermore == gives the correct result since it compares elements memberwise instead of just checking the reference. I recalled that in Java one has to use Equal on strings, since == just compares references. So I googled around and found an explaination in point in the following link at 6.7. Note all the special cases. The best part is the following paragraph: “The implementation of Equals() in System.Object (the one you’ll inherit by default if you write a class) compares identity, i.e. it’s the same as operator==”. Apparently List doesn’t to that, despite their efforts to help, great… So we’ll have to do that ourselves:

public static IEnumerable < tuple < T1,T2 > > zip < T1,T2 >
(IEnumerable < T1 > l1, IEnumerable < T2 > l2)
{
   IEnumerator < T1 > i1 = l1.GetEnumerator();
   IEnumerator < T2 > i2 = l2.GetEnumerator();

   while (i1.MoveNext() && i2.MoveNext())
       yield return new Tuple < T1,T2 > (i1.Current, i2.Current);
}

public static bool sorted_lists_equal < T > (List < T > l1, List < T > l2)
where T:IEquatable < T >
{
   if (l1.Count != l2.Count)
       return false;
   foreach (Tuple < T, T > t in zip < T,T >(l1, l2)) {
        if (!t.first.Equals(t.second))
              return false;
         }
   return true;
}

IEquatable is an interface what basically says that it will compare by value. But even though our Tuple implementation is a struct and thus is a ValueType it doesn’t implement this interface (the Equals method). It instead automatically defines the == operator to work as one expects since it’s a ValueType. So we have to change Tuple:

public struct Tuple < TFirst,TSecond >
: IEquatable < Tuple < TFirst,TSecond > >
{
   public TFirst first;
   public TSecond second;

   public Tuple(TFirst first, TSecond second)
   {
	this.first = first;
	this.second = second;
   }

   public bool Equals(Tuple < TFirst,TSecond > other)
   {
      return first.Equals(other.first) && second.Equals(other.second);
   }

    public static bool operator==(Tuple < TFirst,TSecond > lhs,
    Tuple < TFirst,TSecond > rhs)
    {
	return lhs.Equals(rhs);
    }

    public static bool operator!=(Tuple < TFirst,TSecond > lhs,
    Tuple < TFirst,TSecond > rhs)
    {
	return !(lhs == rhs);
    }
}

The last two functions was added because now that we’re implementing the IEquatable interface the compiler doesn’t seem to want to implement == and !=.

So instead of the following Python code:

a = [(1,"1"), (2,"2")]
b = [(1,"1"), (2,"2")]
a == b

We have to do the big mess above :-/

Check it out if you need some client side web plotting. The graphs are quite nice since they are antialised and with shadows

It’s been a long ride, but now the alpha release is finally ready for public consumption

<do stuff>

svn commit

<do stuff>

svn commit

<I forgot what I had written in last commit log>

svn log (local copy out of date, only shows revision before the first commit)

svn update

svn: Working copy ‘.’ locked
svn: run ‘svn cleanup’ to remove locks (type ‘svn help cleanup’ for details)

Owned