From wagnerc@plebeian.com

Using the strict pragma does not ban all usages of barewords or force
them to resolution as subroutines so that they can fail as an undefined
subroutine.

Tested on Perl 5.22.4 and 5.29.8

Examples​:
$ perl -MO=Deparse,-p,-q,-x20,-P -e 'use strict; print "$^X $^V\n"; my
$string; print split FOO, $string; '
use strict;
print(((($^X . ' ') . $^V) . "\n"));
my($string);
print(split(/FOO/, $string, 0));
-e syntax OK

$ perl -MO=Deparse,-p,-q,-x20,-P -e 'use strict; print "$^X $^V\n"; my
@​list; print sort FOO @​list; '
use strict;
print(((($^X . ' ') . $^V) . "\n"));
my(@​list);
print((sort FOO @​list));
-e syntax OK

Thanks.

From @tonycoz

On Mon, 04 Feb 2019 15​:16​:24 -0800, wagnerc@​plebeian.com wrote​:

Using the strict pragma does not ban all usages of barewords or force
them to resolution as subroutines so that they can fail as an undefined
subroutine.

Tested on Perl 5.22.4 and 5.29.8

Examples​:
$ perl -MO=Deparse,-p,-q,-x20,-P -e 'use strict; print "$^X $^V\n"; my
$string; print split FOO, $string; '
use strict;
print(((($^X . ' ') . $^V) . "\n"));
my($string);
print(split(/FOO/, $string, 0));
-e syntax OK

$ perl -MO=Deparse,-p,-q,-x20,-P -e 'use strict; print "$^X $^V\n"; my
@​list; print sort FOO @​list; '
use strict;
print(((($^X . ' ') . $^V) . "\n"));
my(@​list);
print((sort FOO @​list));
-e syntax OK

split is fixed by my patch in #133822.

sort specially allows for a bareword subname for the sort sub and dies at runtime if the sub named doesn't exist, even if the sub doesn't need to be called​:

$ ./perl -Ilib -e 'use strict; my @​list; print sort FOO @​list; '
Undefined sort subroutine "main​::FOO" called at -e line 1.

Tony

The RT System itself - Status changed from 'new' to 'open'

From @Grinnz

On Mon, 04 Feb 2019 21​:09​:43 -0800, tonyc wrote​:

sort specially allows for a bareword subname for the sort sub and dies
at runtime if the sub named doesn't exist, even if the sub doesn't
need to be called​:

$ ./perl -Ilib -e 'use strict; my @​list; print sort FOO @​list; '
Undefined sort subroutine "main​::FOO" called at -e line 1.

Not entirely true. See #36333, #130178, #133138.

-Dan

From @Grinnz

On Tue, 05 Feb 2019 00​:13​:43 -0800, grinnz@​gmail.com wrote​:

Not entirely true. See #36333, #130178, #133138.

Last one should be #133178

-Dan

From wagnerc@plebeian.com

The behavior of sort() is especially aberrant.

I found an even older ticket! https://rt-archive.perl.org/perl5/Ticket/Display.html?id=3629

This is surely the source of many sideways bugs.

Why doesn't sort() require the & character to name a sorting subroutine just like every other grab of a subroutine?
exists &foo;
defined &foo;
goto &foo;

sort &foo @​list;

Referenced issues: #2305, #7979, #15733, #16548