See also probably obsolete http://bugs.squeak.org/view.php?id=6942
Nicolas
2010/3/30 Levente Uzonyi leves@elte.hu:
On Mon, 29 Mar 2010, Casey Ransberger wrote:
I noticed that the class comment for Set still thinks you can't stick nil in a set. I was going to update it, but I'm a little confused about what's going on in #array.
I'm about to fix the class comments for the HashedCollection hierarchy, but help is always welcome, especially from a native english speaker.
#(#foo # bar #baz nil) asSet array
{nil . nil . nil . a SetElement . nil . #foo . #baz . nil . nil . nil . #bar}
Can I assume that the SetElement is a stand in for the nil item in the Set?
Yes.
See below for what I have so far.
=================================================
As of Squeak 4.1, Sets can contain nil.
I represent a set of objects without duplicates. I can hold anything that responds to #hash and #=. My instances will automatically grow, if necessary, Note that I rely on #=, not #==. If you want a set using #==, use IdentitySet.
Instance structure:
array An array whose non-nil elements are the elements of the set, and whose nil elements are empty slots. There is always at least one nil. In fact I try to keep my "load" at 75% or less so that hashing will work well.
This also applies for Dictionary, so it'd be better in the comment of HashedCollection IMHO.
tally The number of elements in the set. The array size is always greater than this.
Same as above.
The core operation is #findElementOrNil:, which either finds the position where an object is stored in array, if it is present, or finds a suitable position holding nil, if its argument is not present in array,
Same as above, but this is a bit obsolete, #scanFor: is the current lookup method, #findElementOrNil: is only a compatibility method now.
I'd be very important to mention that the objects' hash must not change while they are added to a set, otherwise the set becomes invalid. If that happens #rehash can be used to fix it.
Levente