> Dunno, what method are you looking at? 

I'm looking at BookMorph>>getAllText.  

Actually, the comment says the author thought he was getting Arrays in both
cases but I think he gets an OrderedCollection in the first line:

	allText _ pages collect: [:pg | OrderedCollection new].
	allTextUrls _ Array new: pages size.

> Is the compactness worth it?

Yup, because I'm thinking about writing for a Palm Pilot (Pocket Smalltalk)
where memory is scarce.





--- Bijan Parsia <bparsia at email.unc.edu> wrote:
> On Fri, 20 Oct 2000, Dan Winkler wrote:
> 
> > Thank you.
> > 
> > That's interesting that collect: returns different classes of
> > collections based on the class of the source collection.  When would
> > you want that behavior?
> 
> Er..all the time? #collect, #select, etc. return collection that is
> "like" the receiver. Think of them as being like filter and map in Scheme.
>  
> > I see in this particular method, the next line allocates and Array
> > explicitly.  Is there a reason we want to let collect: decide the
> > class of collection in the first line but use an Array in particular
> > in the second line?
> 
> Dunno, what method are you looking at? Offhand, it's a little hard to
> tell. I don't see any *harm* in using #collect: to initialize the Array in
> the first case. As I wrote, maybe you'll want to modify it in the future.
> 
> You can't use Array class>>#new:withAll: because you'd end up with only
> one OrderedCollectoin, which is clearly not what you want. You could have
> a #new:withAllValuesFrom: or something, that took a block as it's second
> arg, but I'm not seeing a huge gain here.
>  
> > 	allText _ pages collect: [:pg | OrderedCollection new].
> > 	allTextUrls _ Array new: pages size.
> > 
> > Would you say we should change the second line to:
> > 
> >         allTextUrls _ pages collect: [:pg | nil].
> 
> No that's silly, since all slots are niled by default. I *might* say
> 
> 	 allTextUrls _ pages species new: pages size
> 
> *if* I thought that keeping all the colletions the same type were
> important. For all I know, there's a reason to have allTextUrls be an
> Array.
> 
> > As an old C programmer I'd be tempted to go the other way and force them
> both
> > to be Arrays for compactness since I know they're not going to grow.
> 
> Do you? Is the compactness worth it?
> 
> Even if so, I'm still inclined to prefer the #collect: to any more verbose
> version. I mean, what's the *clarity* gain?
> 
> 
> 	 allText _ pages species new: pages size.
> 	"or, allText _ Array new: pages size."
> 	"Gah! I imediately want to do a collect :))"
> 	1 to: pages size do:  [:i | allText at: i do: OrderedCollection new].
> 
> 
> I *never* see this. So, I would *definitely say it's a Smalltalk
> idiom. Frankly, I don't see a bit of clarity gained, and much lost.
> 
> After all, it's not like one is *confused* by the collect into thinking
> it's somehow attending to the pages. It's perfectly *clear* what it's
> doing and why (to initialize allText).
> 
> In the end, when it gets down to it, my rewrite is basically the
> implementation of #collect:!
> 
> 	| newCollection |
> 	newCollection _ self species new: self size.
> 	1 to: self size do:
> 		[:index |
> 		newCollection at: index put: (aBlock value: (self 
> 			at: index))].
> 	^ newCollection
> 
> Why not reuse it? (Follow the once and only once rule ;))
> 
> Cheers,
> Bijan Parsia.
> 


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