2014-12-17 7:42 GMT+01:00 Damien Cassou <damien.cas...@gmail.com>:
>
>
> Le 16 déc. 2014 22:48, "dboeren" <boer...@gmail.com> a écrit :.
> > Off the top of my head, I would be interested in support for "slices"
> > meaning taking being able to treat a subset of a larger
> OrderedCollection as
> > its own OrderedCollection rather than using copyFrom:to: to create a
> > duplicate object to work with. It seems to me that this would be a more
> > efficient method and should not be difficult to implement I think.
>
> Here is an email I sent about that :
>
> I see you are working on new collections for Pharo. That's great news,
> I'm convinced we can do much better (even if what we already have is
> already much better than what can be found in most other languages).
> One thing you could work on is the notion of iterator. There are
> plenty of ways to iterate over a collection:
>
> 1/ from the first to the last item
> 2/ from the last to the first
> 3/ from the 2nd item to the 5th
> 4/ only even items (2, 4, 6, ...)
> 5/ ...
>
> Currently, we have to create new collections to iterate in strange
> ways. For example, to iterate from the last to the first item, we
> create a new collection by sending #reversed to the original
> collection. I think that is bad because it creates a copy and that
> should not be necessary.
>
I don't understand that example. #reverseDo: do not create a copy and do
not send reversed. To iterate over items from last to first I always do, as
recommended in Smalltalk best practice pattern:
mySequenceableCollection reverseDo: [:item | .. ].
#reverseDo: is implemented on SequenceableCollection but iterating from
last to first item does not make sense in the case of non sequenceable
collection.
> What we miss is the notion of iterator. An
> iterator is an object that is specialized in iterating over any kind
> of collection and has methods like #select:, #reject:, #allSatisfy:.
> From a collection, you can access different kinds of iterators
> (reusing the same ordering as before):
>
> 1/ aCollection iterator
> 2/ aCollection reverseIterator
> 3/ aCollection from: 2 to: 5
> 4/ aCollection iterator select: [ :each | each isEven ] --> that
> returns an iterator as well, so you can call #select:/#reject:
> multiple times without creating any intermediate collection
> 5/ ...
>
That makes sense and would be lovely. What is the syntax for multiple
operations ? Have you already think and find something nice about it ?
aCollection iterator
select: [ :each | each isOdd ];
reject: [ :each | each is isPrime ];
iterate
???
Of course there are backward compatibility issue which needs to be very
well adressed here or one would crash every single framework in the system.
> Lukas Renggli implemented a prototype that looks really nice but is
> unfinished: http://source.lukas-renggli.ch/unsorted/Container-lr.7.mcz.
>
> I think the notion of Sequences in Clojure is very related as well.
> Sequence functions are very generic and can be applied to any kind of
> collection. http://clojure.org/sequences
>
