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Good explanation. I'd suggest adding something that explicitly explains how to avoid this problem.

The basic solution is to wrap all top-level code that isn't inside a subroutine in a new sub, and then fixing all the problems with global variables.

In this case, something like:

use strict; use warnings; main(); # <----- change + here sub main { # <----- change + here my $foo = 5; print "Content-type: text/plain\n"; print "Content-disposition: inline; filename=foo.txt\n\n"; printf "Package: %s\n", __PACKAGE__; printf "[%s] Before: %s\n", $$, $foo; badness(5); printf "[%s] After: %s\n", $$, $foo; } # <----- change + here sub badness { my $val = shift; printf "[%s] badness: %s\n", $$, $foo; $foo += $val; }

That will not run, so we need to fix the reference to $foo in badness:

use strict; use warnings; main(); main(); main(); sub main { my $foo = 5; print "Content-type: text/plain\n"; print "Content-disposition: inline; filename=foo.txt\n\n"; printf "Package: %s\n", __PACKAGE__; printf "[%s] Before: %s\n", $$, $foo; badness(5, $foo); # <----- change + here printf "[%s] After: %s\n", $$, $foo; } sub badness { my $val = shift; our $foo; # <----- clever + trick here(*) local *foo = \shift; # <- printf "[%s] badness: %s\n", $$, $foo; $foo += $val; }

Real-life scripts will probably be harder, so make sure to run perl -c your_script.pl early and often :^)

Update: As ikegami pointed out, using my $foo = shift in badness runs, but it doesn't act the same. The (*)clever trick suggested by ikegami is a good way to circumvent that. Later iterations should probably move to a more functional approach, by making the subroutines free of side effects.


In reply to Re: mod_perl / Apache::Registry accidental closures by rhesa
in thread mod_perl / Apache::Registry accidental closures by imp

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