Hi Monks, "strict refs" declaration confuses me. The declaration doesn't allow symbolic references. The following code tries to call, undef and defined subroutines using symbolic references while "strict refs". 
# cat.pl
use strict;
use warnings;

sub walk {}
sub run {}

my $walkable = defined &{ 'walk' };
undef &{ 'walk' };
&{ 'run' };

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The above output the following: 
$ perl cat.pl
Can't use string ("run") as a subroutine ref while "strict refs" in us
+e at cat.pl line 9.

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According to perldiag, the above error message means:
Only hard references are allowed by "strict refs". Symbolic references are disallowed. See perlref.

I understand why the script throws an exception, but I'm not sure why defined/undef &{'walk'} are allowed. Are there any differences?

Sincerely,
Ryo

UPDATE: I noticed &{ 'run' } calls run(), while defined/undef &{ 'walk' } never call walk(). I think that's the difference. PBP written by D. Conway says "18.7 Always use strict". In this section, \&{$DUMP} doesn't violate "strict refs" because the expression doesn't call dump_at(). I thank PBP :-)

NOTE: PBP says "Never use symbolic references". This practice is undoubtedly reasonable.

In reply to undef/defined &{$name} while "strict refs" by anazawa

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