On 12.11.2009, at 13:05, Levente Uzonyi wrote:

> Hi!
> 
> On Thu, 12 Nov 2009, Bert Freudenberg wrote:
> 
>> 
>> 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.
>> 
> 
> What about this?
> (3e): make a class called UnoccupiedSlot with a single instance. Add EmptyFlag to Set, and make sure that EmptyFlag is the instance of UnoccupiedSlot.
> This way the inspector would print "an UnoccupiedSlot" for empty slots and we could save a message send in the implementation.

Which message send would you save in

	... == UnoccupiedSlot

?

- Bert -