On 2008-Jun-1, at 11:20 am, Jon Lang wrote:
David Green wrote:
I thought it already did, but apparently it's something that we discussed that didn't actually make it into S09. I agree that .[] should apply to hashes just as .{} can apply to arrays. The hashes don't even need to be
sorted -- %h[$n] would basically be a shorter way of saying
@(%h.values)[$n], in whatever order .values would give you.

I believe that the order that .values (or is that :v?) would give you is determined by .iterator - which, if I'm understanding things correctly, means that any use of :v, or :k, :p, or :kv, for that matter, would autosort the hash (specifically, its keys).

Or am I reading too much into autosorting?

No, that's my understanding too, with the observation that it doesn't matter whether there's any sorting going on (so the order might be arbitrary -- as in your next point).

Bear in mind that keys are not necessarily sortable, let alone autosorted. For instance, consider a hash that stores values keyed by complex numbers: since there's no way to determine .before or .after when comparing two complex numbers, there's no way to sort them - which necessarily means that the order of :v is arbitrary, making %h[0] arbitrary as well.

Aha -- I guess you're thinking in terms of "autosorting" that can be turned on to return the values ordered by < and >. But .iterator can do whatever it wants, which in the default case is presumably to walk a hash-table (technically not an arbitrary order, although it might as well be as far as a normal user is concerned). Or you could make .iterator return values sorted by alphabetical string- representation (which would work for complex numbers), or you could make it work by using < and > (which wouldn't work with complexes).

Which doesn't contradict anything you've said of course -- but I'm OK with arbitrary orders. If %h[0] is arbitrary, that's fine.

This is why I was suggesting that it be limited to autosorted hashes: it's analogous to how @a{'x'} is only accessible if you've actually defined "keys" (technically, user-defined indices) for @a.

Do you see that as a psychological aid? That is, if the order is arbitrary, %h[0] makes sense technically, but may be misleading to a programmer who reads too much into it, and starts thinking that the order is meaningful.

My feeling is that it's fine for all hashes to support []-indexing. But if the order isn't important, then you probably wouldn't need to use [] in the first place (you'd use "for %h:v", etc.)... so maybe it should be limited. Hm.


P.S. Everywhere I said < and > I really meant .before and .after.  =P

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