On Thu, Nov 13, 2003 at 09:16:59PM -0000, Rob Dixon wrote:
> Steve Grazzini wrote:
>> This is a documented optimization w/r/t foreach() loops, but the same
>> thing applies to the foreach() modifier.
>
> What the code is optimised to is a touch OT, but I've never seen this
> documented Steve. Can you direct me?
It's in perlop under "Range Operators".
In the current implementation, no temporary array is created when the
range operator is used as the expression in "foreach" loops, but older
versions of Perl might burn a lot of memory when you write something
like this:
for (1 .. 1_000_000) {
# code
}
It looks (in the Changelog) like "older versions" means $] < 5.004_069.
> What do you think is happening under the hood for something like
>
> print for (0..0, 1, 2..5, func(6)..func(99))
I think the whole list would have to be generated. The optimization
only applies to the case where there's just one range in place of the
LIST. It's kind of tricky to demonstrate this, though. Running with -Ds
would show it. And there are some bugs with constant ranges:
% perl -e 'for (1,2) { print $_++ for 1..2,3..4; print "\n" }'
1234
2345
When you just have one range, it gets expanded "lazily" and produces the
correct output.
% perl -e 'for (1,2) { print $_++ for 1..4; print "\n" }'
1234
1234
--
Steve
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