Comment by SeanLuke | Hacker News Reader

Comment by SeanLuke | Hacker News Reader

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???

I'm an old NewtonScript coder -- I wrote a JVM for the Newton, for example. NewtonScript is a fairly pure proto-OO language, and it was great to work in. I was thinking of getting into JavaScript, but after reading this article I am shocked, SHOCKED, at how bad JS appears to be.

Class-style OO has really one major advantage: speed. You can do object slot lookups in O(1). Otherwise it's mostly disadvantages: it's very wasteful of memory, it's not dynamic, it mates poorly with functional programming styles, and its unnecessarily complex.

Let me get this straight. JavaScript is proto underneath (and thus is slow), but strives so hard to feel like a Class-style OO that it has deprecated developer access to ITS OWN PROTO OPERATOR. Thus it loses most of the advantages of proto languages except memory consumption, and still has all of their disadvantages.

And this nightmarish condition was all done in order to shield the coming-from-C++ developer from having to "learn" the trivial concept of proto-style OO? And ten years later it's STILL the case?

Yep, you've got that all about right.

There are a couple of fine points: In JS, using regular constructors, object slot lookups still tend to be O(1)-ish -- engines like V8 optimize the "hidden class" of the object by assuming that all instances share the same rough shape, with guard checks if you start to change your properties dynamically later.

Also, regular constructors in JS are much more memory-efficient than the popular alternative "module pattern", which looks like this:

    var makePoint = function() {
      var x, y;
      return {
        getX: function(){ ... },
        getY: function(){ ... },
        distance: function(){ ... }
      };
    };

    var point = makePoint();

Because functions in JS are mutable objects with their own identity, guess what happens each time you create a point? You've just duplicated every function that the point uses as a method, including their closure. It gobbles up memory to the point where you can't make more than a few thousand instances of any object, no matter how small.

With "new Point", in JS, there's only ever one copy of the point's functions in use -- living on Point.prototype -- and all this is avoided.

Finally, class-based OO can be fully dynamic these days, it just depends on how you want to implement it: see Ruby, where any object can have a "metaclass" with its own complement of methods.

I think you are conflating static typing with class-based OO. Python for example is class-based but still fully dynamic. You can mutate classes at runtime, and even replace the class of an instance at runtime, OTOH Python cannot do the slot lookup optimization you speak of, due to its dynamical nature. Python shows that class-based inheritance is very useful (and easy to use) in a dynamic language.

I believe you may have picked the one language which inadvertently illustrates my point.

My understanding is that Python does these things because it's in the SAME bag as JavaScript: it's actually a proto language in implementation down deep, but with a class-based syntax, thus inheriting the disadvantages of both and the advantages of neither. There's some dynamicism bubbling up from the object implementation but it's a far cry from the elegance of a real proto language. I do not know why Guido chose to do this awful thing, but he is at least to be excused given the age of the language. JavaScript has no such excuse.

I guess you could argue that Python is a prototype language deep down because it performs property lookups at runtime by following a chain of objects. (Those objects just happen to be classes.) But by that definition, other dynamic OO languages like Perl or Ruby is also prototype languages.

If you think of classes in Python as a feature build on top of prototypal inheritance, then it has certainly proved a very useful feature.

Exactly, Python is a "prototype-based" language with first-class classes as sugar; similar to Coffee. I gave a link below where kinds of classes are described.

My understanding is that, unlike Python and JavaScript, Ruby has a true class-based OO system. Can't speak to Perl.

That is interesting, I don't know Ruby that well. But by what definition is Python not a "true" class based OO-system?

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