Re^6: undef/defined &{$name} while "strict refs"

When we execute my code above, the script throws an exception because &{ 'run' } violates "strict refs". Khen1950fx explained how to avoid this problem (I appreciate his suggestion).

On the other hand, when we comment out &{ 'run' }, my script doesn't output error messages. This result shows the following doesn't violate "strict refs":

my $walkable = defined &{ 'walk' };
undef &{ 'walk' };
[download]

It seems each line uses symbolic references. I don't understand why this is possible.

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Re^7: undef/defined &{$name} while "strict refs" by Anonymous Monk on Aug 21, 2012 at 08:25 UTC
Well , yes, this part I understood when I answered Re^2: undef/defined &{$name} while "strict refs" The answer according to strict is that its an exception made for AUTOLOAD	[reply]
Re^8: undef/defined &{$name} while "strict refs" by Athanasius (Archbishop) on Aug 21, 2012 at 08:33 UTC
No, here is the relevant quote from the documentation for the strict pragma: `strict refs This generates a runtime error if you use symbolic references (see per +lref). ... There is one exception to this rule: $bar = \&{'foo'}; &$bar; is allowed so that goto &$AUTOLOAD would not break under stricture.` [download] and here is code demonstrating the problem: `>perl -Mstrict -e "sub walk {} sub run {} my $walkable = defined(&{'wa +lk'}); my $runnable = &{'run'};" Can't use string ("run") as a subroutine ref while "strict refs" in us +e at -e line 1.` [download] So, the question is: How does the documented exception for `use strict 'refs'`, which allows use of a reference to a symbolic sub, explain the observed fact that when `defined` is applied to the sub itself (not a reference), no runtime error is raised? Or, conversely: If the expression `&{'walk'}` is legal as an argument to `defined`, why is the expression `&{'run'}` illegal as the right-hand-side of an assignment? How (and why) does Perl distinguish between these two cases? Athanasius <°(((>< contra mundum	[reply] [d/l] [select]
Re^9: undef/defined &{$name} while "strict refs" by Anonymous Monk on Aug 21, 2012 at 08:45 UTC
Ooooooh, well that could be called a bug But if you ask me, both 'run' and 'walk' being string constants, well, I don't see why either &{'run'} or &{'walk'} should be illegal	[reply]
Re^9: undef/defined &{$name} while "strict refs" by anazawa (Scribe) on Aug 21, 2012 at 10:08 UTC
Athanasius clarified what I wanted to say. Thanks a lot :) By the way, the following is equivalent to the code in question: `no strict 'refs'; my $walkable = defined *{ 'walk' }{CODE};` [download] In this case, "no strict refs" is required and it seems reasonable. Should we cosider `defined &{ 'walk' }` not to be a recommended expression?	[reply] [d/l] [select]