[phaedrus]

I agree; to me it says equally as much about the expectations of the author of the article. In C++ you can define operator < and in C# you can define IComparable. Therefore I was astonished to discover the datastructures in the dynamic language Io can't be extended to use custom comparators. It's just an implementation limitation: Io's datastructures are all written in C and so there's a fixed set of types they use for keys. It is what it is.

On the other hand C++ is only just about to get its first version of Concepts. (Haskell programmers in this thread: imagine if you waited 10+ years to get typeclasses.)

My point being that most languages are going to be missing something you wish they had.