I wouldn't say it's that Perl "knows better" so much as that it's a convenience for being able to modify the data you're iterating over.

Note that, because it's only a foreach loop that acts this way, and for is this context is just an alias for the same thing, if you want the behavior you were expecting you can use the 3-arg form of a for loop:

use strict;

my $i = "whatever";

for ($i = 1; $i <= 10; $i++) {
  last if $i == 7;
}

print "$i\n"; # prints "7" instead
[download]

use strict;

my $i = "whatever";

foreach ($i = 1; $i <= 10; $i++) {
  last if $i == 7;
}

print "$i\n"; # still prints "7"
[download]

Very cool.

I was aware that for and foreach are synonyms, but that the 3-arg from of for behaves differently from the list-form with respect to variable localization is entirely new to me - and again unexpected...

Why would these two forms not use the same logic wrt variable localization ... beyond me...

Oh well, just one more wart I guess...

The localization behavior, in my view, is expected and a benefit, not a wart. The only surprise was the localization was transparent and legal, but again, to me, I never would have found out on my own because repurposing variables like that is code smell.

This was often discussed already, have a look into the archives if you want more details.°

IIRC it's because this behaviour of localizing the loop var is older (read Perl4) than lexicals.

Rule of thumb: never try to reuse an outer var as loop var in foreach... see also PBP advice to always for my $x (...) .

°) it leads to very confusing results if the loop creates subs closing over the loopvar.