Joerg Heinicke pisze:
>
> I don't have the time to actually look into your implementation. I'm
> just wondering if all the insight views couldn't be used to improve the
> Java implementation rather than starting something in a different language.
It could.
What I'm doing at the moment is sort of wild experimentation that I don't know
where will lead me to. I'm reimplementing
sitemap in Scala because I thought that sitemap processing is something
complicated enough to get a real feel of
programming in Scala.
It's true that anything I write in Scala could be emulated in Java but when I
think about it I feel rather overwhelmed
by the possible verbosity of Java counterparts to Scala constructs. In my
implementation I exploit heavily strong typing
by defining lots of types and using lots of generics. I use closures and
pattern matching quite a lot.
Compare (Scala):
private def filterUnprefixedSimpleAttributes(attributes : MetaData) :
Map[String, String] =
Map() ++ attributes.flatMap(attr => attr match {
case ua : UnprefixedAttribute => List(ua.key ->
ua.value.first.toString)
case _ => Nil
})
to translation of it (Java):
private Map<String, String> filterUnprefixedSimpleAttributes(MetaData
attributes) = {
return (new Map<String, String>()).putAll(attributes.flatMap(
new Function1<MetaData, List<Tuple2<String, String>>() {
List<Tuple2<String, String>> apply(MetaData x) {
if (x istanceof UnprefixedAttribute) {
UnprefixedAttribute ua = (UnprefixedAttribute) x;
return new List<Tuple2<String, String>>().add(
new Tuple2<String, String>(ua.key(),
ua.value().first().toString()));
} else {
return new List<Tuple2<String, String>>();
}
})
}
And no, I didn't take the most complicated example from my code because I don't
it find funny to write such a spaghetti
code.
So certainly I could write the same in Java but I honestly believe that in Java
operating on strongly typed, immutable
collections is NOT fun and that's the reason nobody seems to do.
And if you skim through my code you'll find that it's more or less only about
mapping, reducing and filtering strongly
typed collections.
Still example above does not prove anything general (like "Java sucks, let's do
it in Scala") but my reimplementation of
sitemap processing should provide a nice background for a discussion what we
want to see in C3.
For example, I'm interested in answering questions like if we are going to
introduce any other language apart from Java
in C3. Traditionally Cocoon had other languages integrated for years
(Javascript comes to mind) so it's rather natural
to ask this question. If answer was positive (based on some evaluation) another
question that pops up is why it can't be
Scala?
WARNING: Here follows some thoughts on personal experience with Scala that you
my safely ignore as they are rather
off-topic.
Might be that I'm extrapolating but my sitemap reimplementation in Scala did
work just after I finished all necessary
bits. I mean: I have written all the processing, integrated it into servlet so
it could work with the rest of C3 and it
did work just immediately. I didn't have any test-cases and I didn't run my
code while writing it.
After extensive testing with all samples C3 provides I found exactly one bug[1]
in that code. Of course, this does not
mean I don't have any other bugs but the probability that I have many of them
is really small.
Does Scala make me magically not making any mistakes? Certainly not. It only
informs me about them at the time of
writing code by reporting compilation errors.
This experience convinced me to have following standpoint:
If we are going to introduce any secondary language in Cocoon,
I would really prefer if it was strongly typed one.
Oh, and if you wonder how on the hell I could be typing non-trivial stuff for
more than one day without introducing
almost any bugs. It might be because my code cotains 5 if statements, no
return, break or continue statements and only a
few raw loops (like "while", "for" or "repeat"). I believe that's the reason...
And yes, I have to admit that sitemap processing is somehow special case where
the power of concepts I've used simply
shines.
[1]
http://github.com/gkossakowski/apache-cocoon3/commit/845f7b61861827a17fb017625eb7f2281ac458df
--
Best regards,
Grzegorz Kossakowski
