Re: [scala-language] The cake’s problem, dotty des ign and the approach to modularity.

On Tue, Jun 16, 2015 at 12:53 AM, Shelby <[email protected]> wrote:

>
> Am I homing in on the generative essence? Nobody has been able to
> succinctly and concretely explain to me why I need Scala and not Haskell
> disregarding the Java compatibility or lazy by default differences.
>
>
This is kind of off-topic for the original thread, but:

Inheritance provides a way to automatically assemble chains of
mutually-dependent functionality without having to worry about the
details.  It's a somewhat fragile solution, but nothing other than
extremely late binding via (something computationally equivalent to) vtable
lookup really does the trick.

So if you have, for example, a bunch of drawable windowing components with
all sorts of elaboration therein, you can still have a xs: List[Component]
and get something sensible with xs.sortBy(_.zDepth).foreach(draw).

It's not the only way to solve the problem at all, since any problem you
can solve with inheritance you can also solve with composition, but with OO
it's really easy to make most everything overridable so you have to go back
and modify your library less often.  (Unfortunately, due to a lack of a
really robust way to specify logical dependencies, you often need the
source code to the library anyway so you know what is safe to override
alone, what must be overridden in pairs, etc.).

It also doesn't play terribly nicely with immutability because you lose
track of which constructor you ought to use.  The whole _point_ of OO is to
lose track so you don't have to worry about it, but then when you need to
worry...well...you're stuck.  A classic example is

  List(new A, new A{ override def foo = "different" }).map(x.asCapitalA)

If `asCapitalA` has mutating side-effects, you retain the distinct `foo`
behavior.  If, in contrast, it creates a new immutable A, your unique `foo`
behavior is lost.

So you might just reject OO as a tool that helps you most in a situation
that you avoid anyway.  But that doesn't mean that there are equivalently
easy functional or monadic or other ways to do the same thing.  Everything
else is harder.

  --Rex

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