[squeak-dev] Re: Want: #slice: (Re: Noob question: array slice?)

Bert Freudenberg bert at freudenbergs.de
Sat Aug 7 10:29:46 UTC 2010


On 07.08.2010, at 05:56, Andreas Raab wrote:

> On 8/6/2010 6:20 PM, Igor Stasenko wrote:
>> On 6 August 2010 17:45, Randal L. Schwartz<merlyn at stonehenge.com>  wrote:
>>>>>>>> "Casey" == Casey Ransberger<casey.obrien.r at gmail.com>  writes:
>>> 
>>> Casey>  It's literally adding a method to make the cuneiform smalltalk
>>> Casey>  crap accessible to new people, who are liable to search on terms
>>> Casey>  like 'slice.'
>>> 
>>> What you are asking for is something that would be useful for only
>>> those first few hours, and then be a maintenance clutter for the
>>> remaining years of programming.
>>> 
>>> I vote "-1".
>>> 
>> +1 to your -1.
> 
> I vote -2 on your -1 which should leave us at +0 I think :-)=)
> 
> No, seriously. I think there's actually a pretty good and generic interpretation of slice if you consider it to be an operation that can collect arbitrary sequences. For example:
> 
> Collection>>slice: aCollection
> 	"Slice the receiver by aCollection, collecting all elements
> 	in the receiver that are keyed by aCollection."
> 
> 	^aCollection collect:[:each| self at: each] as: self species.
> 
> With a polymorphic implementation this would allow some interesting uses that are quite difficult to implement otherwise, for example:
> 
> 	dd := Dictionary newFromPairs: {
> 		'firstName'. 'Joe'.
> 		'lastName'. 'Sixpack'
> 		'dob'. '01-01-2001'.
> 		'zip'. '12345'
> 	}.
> 	dd slice: #(firstName lastName).
> 
> This would return a dictionary with only firstName and lastName. And of course, when used with intervals it would behave identical to #copyFrom:to: just somewhat less efficient, but that's offset by, say, uses such as:
> 
> 	"Slice out all the odd elements"
> 	aCollection slice: (1 to: aCollection size by: 2).
> 
> Etc. So I think the argument for #slice: can be made and we should consider it as a more generic operation instead of just a slower version of #copyFrom:to:.

But we have that already. It's called #atAll: which is nicely consistent with the rest of the collection protocols. We just need to add a more generic version in Collection.

- Bert -





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