"Stephen P. Potter" <[EMAIL PROTECTED]> writes:
> Lightning flashed, thunder crashed and Russ Allbery <[EMAIL PROTECTED]> whispere
> d:
> | > Arrays are ordered. Hashes are not. Sure, you can iterate over a hash,
> | > but add an element to one and you can change the order of everything in
> | > it.
> |
> | Formally, I believe it's permissable for a hash implementation to return a
> | different order the second time you iterate through it from the first
Actually not. See "perldoc -f values":
] ...The actual random order is
] subject to change in future versions of perl, but it is guaranteed to
] be the same order as either the C<keys()> or C<each()> function would
] produce on the same (unmodified) hash...
>
> What stops us from imposing order on this chaos? If they are currently
> defined as not having any specific order, why can't we say they always
> return in numeric || alphabetic || ASCII || whatever order we want?
Efficiency. If I just want to map over all elements stored in a hash,
I just want the fastest access to all the elements. If I want to
access the hash by ASCII order of keys, I can `sort keys %hash'.
Think of the keys as being returned in some "efficient" order. The
specific "efficient" order is not specified, but it's guaranteed to be
a fast way to iterate over all keys.
> The internal storage implementation can be kept seperate from the external
> interface. A hash *should* be able to be advantageous over an array in
> just about all respects, except maybe size. And, we've shown how a sparse
> array can be handled in a hash without any special machinations.
for (@array) {
# stuff with $_
}
is fast.
for (values %hash) {
# stuff with $_
}
(or the roughly equivalent for loop with `keys %hash' and while loop
with `each %hash') is fast.
for (sort keys %hash) {
# stuff with $hash{$_}
}
is not so fast. So defining a sorted order would negate the advantage
of hashes over arrays you refered to.
It seems like a tied hash would be suitable for what you want. If
ties were efficient, it would be trivial to implement a SortedHash
which would perform "each"-style accesses in sorted order. Standard
Perl library, anyone?
--
Ariel Scolnicov |"GCAAGAATTGAACTGTAG" | [EMAIL PROTECTED]
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