On Fri, Aug 23, 2013 at 11:22:47AM -0700, Sean Kelly wrote: > On Jul 31, 2013, at 7:55 AM, Dicebot <pub...@dicebot.lv> wrote: > > > On Wednesday, 31 July 2013 at 14:43:21 UTC, Daniel Kozak wrote: > >> is there a way for AA to behave same as PHP? > > > > I doubt it. This snippet suggests that AA's in PHP are not simply > > AA's and do additionally track insertion order (or use some similar > > trick). Data in associative arrays is organized in a way that allows > > fast key lookup and iterating in an original order requires tracking > > extra state. Contrary to PHP, D does care about performance so I see > > no way this can happen automatically. > > This seems more likely to be a library type. I have something like > this that I use very frequently at work where the behavior is > pluggable, so it can be used as a cache that automatically does > LIFO/FIFO eviction according to an age window, number of entries, etc. > Or none of those if all you want is a plain old hashtable. It's not a > tremendous amount of work to adapt an existing implementation to work > this way. The only annoying bit I ran into (at least with C++) is > that the symbol lookup rules pretty much prevent overrides of existing > functions to be mixed in via the policies. Does alias this work > around this problem in D? I've never tried.
In http://d.puremagic.com/issues/show_bug.cgi?id=10733 bearophile and I discussed code reuse between the current AA and an ordered AA implementation. It appears that a more fundamental structure is the Set, where the key is the value. An AA can be implemented in terms of a Set, by making the set element a struct containing a key and value field, with a custom toHash() and opCmp() that only hashes/compares the key part. By adding a pair of pointers to this customized set element, we can make an ordered AA in terms of Set. Plus, a Set is something that's very useful on its own as well. T -- Береги платье снову, а здоровье смолоду.
