What are the advantages that prototype based OO has over class based OO?

Question

Why is class based OO so popular instead of prototype based OO? Do they teach the latter in schools? Though Javascript is prototype based, most people use it mostly functionally, or via frameworks that try to emulate a class based system.

I know that Sun has had some research on Self - is there any other source of knowledge on prototype based oo? preferably something that is accessible for self learned.

I found a book that contains published papers: Prototype-Based Programming: Concepts, Languages and Applications

Has anyone read it?

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So I gave the bounty for the answer that gave me most. Still, I'm not really satisfied. I would have liked to hear much more techical answers. Maybe I didn't explain myself well.

Answer 1

The advantage of prototypal inheritance is that it potentially allows fancy metaprogramming in a straightforward way because the prototype chain is easily manipulated. This is a rather academic advantage because metaprogramming is the wrong answer 99% of the time. As an example, you could have a Javascript Key-Value Observer style data manipulation layer with a special DSL that transparently switched between a local SQLite backing when offline and a REST based server store when online via prototype swapping. I'm not sure it's the best way to do this, but it's the best I can come up with this late. It's not the sort of thing you generally want to do in project code since this sort of indirection is hell to debug once you start getting it going on multiple layers, but it's not bad when you keep it in a library.

Another less helpful advantage is that it allows you to design your own class system. I say less helpful because more or less all javascript libraries have their own slightly incompatible approach to how 'classes' are put together.

There are a lot of people replying who are mixing the inheritance model with the languages implemented in that model. The fact that javascript is dynamic and weakly typed and thus hard to tool has nothing to do with it being a prototypal language.

Answer 2

If you're looking for someone to point out the advantages/disadvantages of each as an explanation for their popularity, I think you're falling for a fallacy which is for some reason very common in technology - that popularity has something to do with some absolute measure of quality.

The truth is a lot more bland - class based OO is popular because Java uses classic OO, and Sun spent millions of dollars and a very long time building the popularity of Java - making sure people know it's used successfully in corporations, taught widely in universities, and on high school AP tests.

Prototypal/classical OO are just different ways of organizing your ideas. You can implement either one in languages that don't support it natively (Python and Java come to mind, and JavaScript on the other side).

In classical OO, you define an abstract hierarchy of classes for your objects, and then actually work with instances of those classes. In prototypal inheritance, you create a hierarchy of object instances. Although I imagine it might be a bit heretical in both camps, I don't see a reason you couldn't mix the two...