On Wed, 3 Sep 2014, Clément Bera wrote:
Hello guys,
I was looking into the OrderedCollection protocols recently to see how well the
sista optimizer perform with it methods, and I realized that this is completely
broken.
For example:
col := #(1 2 3 4 5) asOrderedCollection.
col do: [ :elem | elem trace .
elem < 4 ifTrue: [ col add: col size + 1 ]].
=> '12345678'
However:
col := #(1 2 3 4 5) asOrderedCollection.
col collect: [ :elem | elem trace .
elem < 4 ifTrue: [ col add: col size + 1 ]].
=> '12345'
This means that #do: and #reverseDo: iterate over all the elements of the
collection,*including* the ones that you are adding while iterating over the
collection, whereas all the other OrderedCollection
protocols, such as #collect:, #select:, iterates over all the elements of the
collection, *excluding* the ones you are adding while iterating over the
collection.
In case of #select and #collect: this is only true for elements added with
#addLast:, #addFirst:, or #add:, but there are other methods which can
have (even worse) side effects (#add:after:, #add:before:, etc).
Levente
Marcus argued that one should not edit a collection while iterating over it,
however this point is not valid as the World menu relies on this feature, using
#do: to iterate over the elements of the
OrderedCollection including the one it is adding while iterating over the
collection. Changing the implementation makes the world menu display half of
its items.
I don't like this difference because it is inconsistent. For example,
refactoring a #do: into a #collect: can simply not work because they do not
iterate over the same elements if you are editing the
collection while iterating over it.
In VW, the protocols are consistent and iterating over a collection never
iterates over the elements one is adding while iterating over it. Therefore, I
believe most frameworks should expect this behavior (at
least the ones cross smalltalk) which sounds the most correct.
I think we should fix the world menu implementation and make the protocols
consistent. Alternatively, we can let VW be a much more consistent Smalltalk
environment than Pharo. What do you think ?
Clement
