Hi all Smalltalkers!

Only cross posting to squeak and pharo (communities I know), because 
this turned into a long post. But try reading it - I hope it is both fun 
and perhaps interesting. :)

On 02/11/2012 01:21 PM, Janko Mivšek wrote:
> Hi guys,
>
> Again one interesting topic for this weekend to discuss. David Nolen, a
> Lisp and JavaScript guy posted in his blog an article titled Illiterate
> Programming [1] where he said:
>
> "...Yet I think Smalltalk still fundamentally failed (remember this is a
> programming language originally designed to scale from children to
> adults) because *Objects are really hard* and no-one really understands
> to this day how to do them right...."

As Hernan pointed out - it is programming that is hard, not *objects* 
per se. While that is true, one can of course still reflect on the 
aspects of OO and why people *perceive* it as hard.

SIDENOTE: As Milan wrote later in the thread - the patterns movement 
that Kent Beck started together with the Gang of Four led to the 
creation of TONS of books fully packed with OO designs in various 
domains. So yes, there is an *abundance* of books on OO design to find 
*iff* one goes looking for it.

> He links to Alan Kay post [2] back in 1998 where he talks about problems
> with inheritance:
>
> "Here are a few problems in the naive inheritance systems we use today:
> confusions of Taxonomy and Parentage, of Specialization and Refinement,
> of Parts and Wholes, of Semantics and Pragmatics..."

Of all OO mechanisms most agree that inheritance is the one that gets 
abused the most... if we disregard the "abuse" one can find in so called 
OO code that stems from it not being OO at all :)

Alan writes "confusions" and I suspect he carefully avoids saying one is 
wrong and the other is right, because its not that simple. Truth is one 
can use inheritance differently - as long as it makes your life better 
it can't really be argued to be "wrong". :)

I think most OO developers goes through some "ladder of enlightenment" 
going something like this:

0. You really have no clue and tend to confuse composition "parts and 
whole" with inheritance. You just create a mess. Perhaps you avoid this 
mess by reading a book or attending an OO course, but hey, who does that 
in 2012? ;). But let's say you *do* read a book - proceed to level 1...

1. You get all into Animals and other "inheritance" examples mirroring 
the real world. Perhaps you get totally sucked into the "mirror the real 
world"-idea. Thus, you try desperately to find "ISA" relations among the 
domain objects and use those for inheritance, without really thinking 
*why* that is a good idea. And sure, it often gets it fairly right so 
it's a huge step forward. But let's pretend you now have coded quite a 
bit and thus proceeds to level 2 :)

2. Specialization. After some time you start to understand polymorphism 
and the substitution principle etc, so instead of blindly testing if "A 
isa B" sounds right in your ears you start thinking in terms of 
generalisation and specialization. And you see objects in your head. You 
talk about them as if they are concrete and you can hold them in your 
hand etc. Perhaps you even draw them on whiteboards and envision them in 
different scenarios "talking to each other". If you use a statically 
typed language this is where your road stops :). You end up writing 
fairly good code, but your inheritance will probably be totally focused 
on enabling polymorphism between objects, which of course is not all 
bad. But hey, after a few years of Smalltalking - proceed to level 3.

3. As a seasoned Smalltalker you eventually come down from your "OO 
rush" and realize that... hey, wait a minute! Polymorphism is not *tied* 
to class inheritance (unless you are trapped in some static type 
system). In fact, you realize that class inheritance in Smalltalk is 
"merely" a nice way of reducing the redundancy of code by creating 
dependencies between separate abstractions of code. This realization 
enables you to use inheritance in a more liberal fashion - which 
probably means you tend to use it *less*. And instead you tend to "add 
more objects" and use composition of objects more and more, relying on 
brittle deep hierarchies of inheritance less and less.

SIDENOTE: A really cool example of how powerful object composition is: 
PetitParser by Lukas. For years we have been creating parsers by 
generating code from specifications and suddenly Lukas decides that hey, 
why not instead *compose* a parser from ...objects? It is so obvious in 
retrospect, but the result is a tremendously nicer and more powerful way 
of constructing parsers.

You also conclude that while you *can* reuse behaviors and compose 
behaviors using inheritance you are also aware that inheritance creates 
a life cycle *dependency* between classes that you *may* or *may not* 
want to have. Class inheritance is a brittle relation. Thus, even if 
class A *can* inherit from B, you might decide not to - because you 
anticipate that the development lineage will diverge, or perhaps you 
have no control over A (library? other developer? bad code?), and you do 
not want that dependency. But the up side is that sometimes you *really* 
want that dependency, change superclass and bam - affect all subclasses.

Another obvious benefit of inheritance is of course "documentation 
structure" that you and other developers can understand.

...well. Of course, the above was written sloppily and can of course be 
refined or totally shot down. Feel free to do both! :)

regards, Göran

PS. Why oh why did Pharo lose the "double click on ? in the class 
browser to see inheritance textually"-mechanism? :)