It seems to me that Object>>species is intended to handle this sort of issue.

For IdentitySet, it answers what Eliot was expecting:

   IdentitySet new species ==> IdentitySet
   Set new species ==> Set

However, IdentitySet>>collect: does not make use of this, and it answers
a Set for the reasons that Levente explained.

Answering an Array or and OrderedCollection would not really make sense,
because sets are unordered collections (but Bag might be better).

Shouldn't we have an implementation of IdentitySet>>species that answers
Set (or Bag), with a method comment explaining why this is the case, and
with all of the collection methods using #species to answer the right
kind of result?

I note that IdentitySet>>collect: answers a Set, but IdentitySet>select:
sends #species and therefore answers an IdentitySet.

So I think that if we want the #species of an IdentitySet to be a Set,
then we should make it so, and give it a method comment to explain the
rationale. And the #collect: and #select: methods should both answer a
result of that #species.

Dave


On Thu, Nov 27, 2014 at 01:14:30AM +0100, Levente Uzonyi wrote:
> Your example hides the problem of ordering - what Tobias is asking about - 
> so here's another:
> 
> (IdentitySet withAll: #(1 1.0)) collect: [ :each | each class ]
> 
> If IdentitySet >> #collect: were returning an Array, then what would be the 
> answer?
> 
> { SmallInteger. Float } or { Float. SmallInteger } ?
> 
> If you really want to have the resulting collection have the same size, 
> but avoid the problem with ordering, then what you really need is a Bag.
> Luckily you can have whatever you want (as long as it makes sense):
> 
> (IdentitySet withAll: #(1 1.0)) collect: [ :each | each asInteger ] as: Set.
> "==> a Set(1)"
> (IdentitySet withAll: #(1 1.0)) collect: [ :each | each asInteger ] as: 
> IdentitySet.
> "==> an IdentitySet(1)"
> (IdentitySet withAll: #(1 1.0)) collect: [ :each | each asInteger ] as: 
> Array.
> "==> #(1 1)"
> (IdentitySet withAll: #(1 1.0)) collect: [ :each | each asInteger ] as: 
> OrderedCollection.
> "==> an OrderedCollection(1 1)."
> (IdentitySet withAll: #(1 1.0)) collect: [ :each | each asInteger ] as: Bag.
> "==> a Bag(1 1)"
> (IdentitySet withAll: #(1 1.0)) collect: [ :each | each asInteger ] as: 
> IdentityBag.
> "==> an IdentityBag(1 1)"
> (IdentitySet withAll: #(1 1.0)) collect: [ :each | each asInteger ] as: 
> Heap.
> "==> a Heap(1 1)"
> 
> Levente
> 
> On Thu, 27 Nov 2014, Frank Lesser wrote:
> 
> >Hi Tobias,
> >agree, a problem of "OrderedCollection"
> >not to break a lot of other things we could return an Array.
> >but for me collecting has priority.
> >Frank
> >
> >-----Urspr?ngliche Nachricht-----
> >Von: squeak-dev-bounces at lists.squeakfoundation.org
> >[mailto:squeak-dev-bounces at lists.squeakfoundation.org] Im Auftrag von 
> >Tobias
> >Pape
> >Gesendet: Donnerstag, 27. November 2014 00:48
> >An: The general-purpose Squeak developers list
> >Betreff: Re: [squeak-dev] IdentitySet>>collect:
> >
> >
> >On 27.11.2014, at 00:34, Frank Lesser <frank-lesser at lesser-software.com>
> >wrote:
> >
> >>hmm, not convinced
> >>
> >>(IdentitySet withAll: #(1 1.0)) collect: [:e| e asInteger ]
> >>OrderedCollection(1 1 )
> >>
> >>in LSWVST ( one-to-one ), you collect results of evaluating a block on
> >>objects.
> >>
> >>Frank
> >>maybe I am wrong ...
> >
> >Where would the order come from for that _Ordered_Collection?
> >
> >Best
> >	-Tobias
> >