Sorry to repost, seems that gmane did not like my first attempt...
Stéphane Ducasse <stephane.duca...@...> writes:
>
>
> On Dec 29, 2008, at 12:23 PM, Alexandre Bergel wrote:
>
> > Dear List,
> >
> > I was wondering whether I am the only one shocked when I see this:
> >
> > (Set new add: #b -> 'B'; yourself) includes: #b -> 'B' ====> true
> > (Set new add: #b -> 'B'; yourself) includes: 'B' ====> false
>
> this is correct
>
> > (Dictionary new add: #b -> 'B'; yourself) includes: #b -> 'B'
> > ====> false
> > (Dictionary new add: #b -> 'B'; yourself) includes: 'B' ====> true
>
> we should check the semantics of includes:
>
> > Dictionary inherits from Set. This means that if Set would have a
> > contract, it would break in Dictionary.
> > IMO, we should have
> > (Dictionary new add: #b -> 'B'; yourself) includes: #b -> 'B' ====>
> > true
> > (Dictionary new add: #b -> 'B'; yourself) includes: 'B' ====>
false
> >
> > No?
>
> Dictionary and Set relationship is subclassing so a lot can be strange.
> We should fix that in Bloc.
>
From the st80 origin, Dictionary is a Bag of values.
Each value of this Bag is indexed with a unique key.
It is a Bag because:
a) multiple values can be in the dictionary:
(Dictionary new) at: 'one' put: 1; at: 'first' put: 1; yourself.
b) values are unordered:
| d1 d2 |
(d1 := Dictionary new: 3) at: 'one' put: 1; at: 'two' put: 2.
(d2 := Dictionary new: 4) at: 'one' put: 1; at: 'two' put: 2.
stream := (String new: 64) writeStream.
d1 do: [:v | stream print: v; cr].
d2 do: [:v | stream print: v; cr].
stream contents.
And as you can see, #do: does apply on values, as would #collect:
#select: #reject: #includes: etc...
The fact that Dictionary is implemented with Associations could be seen
as a private implementation-defined feature.
Though, by tradition, associationsDo: has been made a public interface,
so as the possibility to directly add an Association.
But semantically, Dictionary is not a Set of Associations.
Example:
(Set new) add: $a->65; add: $a->1; yourself.
(Dictionary new) add: $a->65; add: $a->1; yourself.
Dictionary could be viewed as a Set of keys.
From that POV, it shared enough property with Set to be implemented as
a subclass. That's all.
I proposed once to detach Set and Dictionary and derive them from a
common ancestor just for
clarity...
Nicolas
_______________________________________________
Pharo-project mailing list
[email protected]
http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
