[squeak-dev] Re: Sets with nil (Was: Ideas about sets and dictionaries)

Bert Freudenberg bert at freudenbergs.de
Thu Nov 12 10:35:33 UTC 2009


On 12.11.2009, at 09:42, Andreas Raab wrote:

> Levente Uzonyi wrote:
>> But we now have a lot more proposals, let me summarize them all:
>> - (1)add a new instance variable: containsNil
>> - (2)use tally to indicate if nil is in the set
>> - (a)negative values mean nil is contained by the set
>> - (b)floats - (3)use a marker object
>> - (a)self
>> - (b)a unique object in each set
>> - (c)a class variable
>> - (4)use container objects in occupied slots, like associations in dictionaries
>> I prefer 3c, 2a, 3a, 1, 4 in the given order.
>> What about you?
> 
> Nice summary. My current preferences would be (1) (clear and obvious) (3b) (ditto) and (3a)/(3c) (both with some hesitation). I'm not sure about (4) (I've only just heard of it; it sounds cool but I haven't seen no code yet). I would veto both (2a) and (2b) as obscure hacks compared to (1) unless the size overhead is significant.

I'd prefer (3d): make a class called UnoccupiedSlot, use it as marker (either the class itself [I'd like that] or its singleton instance [for the purists]). This would make it blatantly obvious what's happening when inspecting the innards of a Set.

I'd reluctantly accept (1) but fear it would complicate the logic - containsNil checks will have to be scattered all over the place.

- Bert -





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