Hi Peter - yes of course you are right that its malleable, I guess I’m often suprised about the things we leave out and then discover weird things we’ve put in.
I had a quick look at LinkedList (I should have thought of that) - I might be able to do something with that (and this is now more out of curiosity) - but gosh its an easy way to crash your image. Having linked the first to the last, and then tried a quick: list after: $n - I’m now guessing I’m stuck in an infinite loop that even Cmd . won’t break out of!!!! ouch. Tim > On 29 Mar 2019, at 10:20, Peter Kenny <pe...@pbkresearch.co.uk> wrote: > > Tim > > But the beauty of Smalltalk is that, if you need to use a particular > structure frequently, you can make it an object just by subclassing > something useful. In this case, you could create CircularList by subclassing > SequenceableCollection and re-implementing #before and #after (and maybe > tidying up #add if you don't want the circle to be extendable). > > Pursuing this line of thought, we already have one specialized subclass in > LinkedList. If the last element is linked to the first, this becomes > circular. I glanced at some of the methods to see how well this would work, > but because it regards links as separate from the linked objects, it got too > complicated. But it could give a starting point if you have lots of such > cases. > > HTH > > Peter Kenny > > > Tim Mackinnon wrote >> Hey thanks guys - while it certainly makes sense when you think about it, >> I was kind of hoping we had something that was much more readable and >> obvious. It seems strange that when we have lots of esoteric things in >> collection, that something which is quite common to do isn’t there. I was >> kind of hoping we might have some circular list or something. >> >> As it stands, if you really want to communicate this clearly you are >> almost better off just doing, the more obvious: >> >> (Index := index - 1) = 0 ifTrue: [index := items size]. >> >> Anyway, an interesting one. >> >> Tim >> >>> On 28 Mar 2019, at 16:55, Peter Kenny < > >> peter@.co > >> > wrote: >>> >>> Tim >>> >>> I found myself puzzling as to *why* James's solution works. This longer >>> explanation helped me to understand. >>> >>> First, generalize moving forward to moving an arbitrary number of steps, >>> still with wrapping. >>> >>> ^list at: (index + move - 1 \\ size + 1 >>> >>> Second, realize that moving backward one step with wrapping is exactly >>> equivalent to moving forward (size - 1) steps - because of wrapping, a >>> move >>> of size steps is null. >>> >>> Finally, substitute move = size - 1. >>> >>> ^list at: (index + size - 2 \\ size + 1. >>> >>> This can of course easily generalize to backward moves of any size. >>> >>> HTH >>> >>> Peter Kenny >>> >>> >>> >>> -- >>> Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html >>> > > > > > > -- > Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html > <http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html>
