[squeak-dev] IdentitySet>>collect:

Chris Muller asqueaker at gmail.com
Sat Nov 29 19:04:14 UTC 2014

On Sat, Nov 29, 2014 at 12:26 PM, Florin Mateoc <florin.mateoc at gmail.com> wrote:
> On 11/29/2014 9:55 AM, Levente Uzonyi wrote:
>> On Fri, 28 Nov 2014, tim Rowledge wrote:
>>> On 28-11-2014, at 6:05 PM, Levente Uzonyi <leves at elte.hu> wrote:
>>>> I think the conclusion was that it's better to leave the method as it is, because there's no better way to do it.
>>> There’s *always* a better way to do it. Somebody just has to think about it the right way.
>> There are too many factors for a better solution to exist.
>> Let's say we change the method to return a Bag. Some will say it's better that way, because the resulting collection
>> has the same size as the original.
>> And some people will say that you broke their code, because the following will return false instead of true:
>> | s t |
>> s := #(1 2 3) asSet.
>> t := s collect: [ :each | each ].
>> s = t
>> IMHO the best solution is still to replace sends of #collect: with
>> #collect:as:, but it's a lot of work.
>> Levente
> I don't understand why anybody would think s should be equal to t in this example.
> collect:, or map as it is called in other languages, maps the elements in the receiver collection, to elements in the
> result, based on the mapping function provided as a block argument.

I've never regarded collect as a mapping function, only a
transformation function.  If I want a map of the original to the
transformed, it doesn't need to be built into the collect: method
itself to do that:

#(1 2 3) collect: [ : each | each -> each asWords ].

There, you have a mapping without needing to change collect:.

> Conceptually, collect: is closer to returning a keyedCollection (which is also called a map), where the keys are the
> elements and the values are their mappings.
> If we see it this way, it is obvious that the order of the original elements is irrelevant, it is also obvious that the
> number of mapped values is/has to be the same as the number of elements (keys), and it is also obvious that the kind (or
> species) of collection holding the original elements (keys) is also irrelevant to the kind of collection holding the
> values. That's why always returning say an orderedCollection is fine, as long as we can map the collected values back to
> the original elements - even using a (long-term unstable) iteration order.
> When the original collection is a sequenceableCollection, we can shortcut all this by just relying on the indexes, which
> index both the original elements and their mappings. But that is not because the original order is itself important for
> the collect operation.

Perhaps we need an #asDictionary method to implement the "mapping"
use-case.  As far as #collect:, however, I find myself agreeing with
Levente.  #collect: is simply too entrenched to change on a whim.  It
appears that #collect:as: can address a variety of additional

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