On 20 August 2012 21:54, Levente Uzonyi <leves at elte.hu> wrote:
> On Mon, 20 Aug 2012, commits at source.squeak.org wrote:
>
>> Frank Shearar uploaded a new version of Collections to project The Inbox:
>> http://source.squeak.org/inbox/Collections-fbs.489.mcz
>>
>> ==================== Summary ====================
>>
>> Name: Collections-fbs.489
>> Author: fbs
>> Time: 20 August 2012, 4:51:36.018 pm
>> UUID: d1834809-65b5-46c0-9b26-fea7ec04a946
>> Ancestors: Collections-ul.488
>>
>> SequenceableCollection >> flatten turns a nested SequenceableCollection -
>> a collection of collections of ... -  into a simple collection. Thus, #(1 (2
>> 3) (4)) flatten = #(1 2 3 4).
>
>
> #flatten was discussed several times, even we (Balázs and me) implemented it
> once, see Collections-klub.130.mcz in the Treated Inbox. I think our
> implementation is better, because
> - it uses #flattened as selector
> - it uses double dispatch
> - it works well with Strings (try #('foo' ('bar')) flatten )
> But I wouldn't push either version to the Trunk now. I could imagine an
> implementation which does the iteration with double dispatch and uses a
> separate method for Array creation.

OK. I didn't mean to suggest that #flatten was useful only for Arrays.
They're just a convenient thing to use for examples: literal syntax. I
hadn't really thought of collections of Strings. I'm not sure why
double dispatch is particularly useful, unless you're thinking of
being able to flatten arbitrary objects - turning a Person into
{#name. 'Frank'}.

> Btw, I usually use #gather: when I need to flatten a level on a collection.
> Deeper than two-levels collection structures are pretty rare in Smalltalk. I
> guess this is why there's no #flatten yet.

I was using a two-level collection, so I reckon I'll just remember
#gather:. More convenient than using (foo collect: #something) inject:
Array new into: #, all the time, which is what drove this
implementation in the first place.

frank

> Levente
>
>>
>> =============== Diff against Collections-ul.488 ===============
>>
>> Item was added:
>> + ----- Method: SequenceableCollection>>flatten (in category 'copying')
>> -----
>> + flatten
>> +       | recur stream |
>> +       stream := WriteStream on: (Array new: self size). "A lower bound
>> on the final stream count."
>> +       recur := [:coll | coll
>> +               do: [:each |
>> +                       each isCollection
>> +                               ifTrue: [recur value: each]
>> +                               ifFalse: [stream nextPut: each]]].
>> +       recur value: self.
>> +       ^ stream contents.!
>>
>>
>
>
>