Re: does a hash element as a loop parameter cause significant slowdown?

for my $c (1..$n1) {
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The list 1..$n1 is created in memory and then iterated over so $n1 is only evaluated once.

If you instead used a C style for loop then $n1 would be evaluated $n1 times.

Naked blocks are fun! -- Randal L. Schwartz, Perl hacker

Comment on Re: does a hash element as a loop parameter cause significant slowdown? Download Code

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Re^2: does a hash element as a loop parameter cause significant slowdown? by LanX (Saint) on Sep 08, 2023 at 23:34 UTC
> `for my $c (1..$n1) {` > The list 1..$n1 is created in memory and then iterated over so $n1 is only evaluated once. Nitpick: you are right that $n1 is only evaluated once, but only old versions "created" the whole "list in memory". This was optimized away ages ago to allow `$a..$b` to act like an iterator. Maybe 5.10ish? > 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... Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^3: does a hash element as a loop parameter cause significant slowdown? by pryrt (Abbot) on Sep 09, 2023 at 00:00 UTC
Maybe 5.10ish? I checked perldoc.perl.org's 5.10 docs: it still had the "but older versions" comment. So I checked 5.005's docs: it still had the "but older versions" comment. So if perldoc.perl.org's copies of the docs are accurate, it was documenting the list-in-memory behavior as "old" even at 5.005! /me guesses he needs to get over his aversion to large ranges in foreach loops ;-)	[reply]
Re^4: does a hash element as a loop parameter cause significant slowdown? by LanX (Saint) on Sep 09, 2023 at 12:19 UTC
Yeah ... I already noticed this, but gave up searching the deltas because I started in the 5.8 era and remember being told about the "problem" But now I found it in the delta of 5.005 > foreach (1..1000000) is now optimized into a counting loop. It does not try to allocate a 1000000-size list anymore. It's the oldest available delta, which probably means only Perl4 had the issue. Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply]