Re^2: 5.24 -> 5.28 -- what has changed in autovivification?

[leszekdubiel]

Thank you for hints. I will check diver module.

PS. In case anybody has the same problem versions were from Debian Stretch and Buster installations:

 

# command: 
# perl -e 'print $], "\n"; ' ; dpkg -l | egrep autovivifi


# Debian buster: 
5.028001
ii  libautovivification-perl          0.18-1+b1                    amd
+64        pragma for lexically disabling autovivification


# Debian stretch: 
5.024001
ii  libautovivification-perl          0.16-1+b2                       
+  amd64        pragma for lexically disabling autovivification

[swl]

The changes file does not list anything obvious to me.

The git repo listed in the module info unfortunately seems not to be accessible.

I'm not sure if it helps shed any light due to the refactoring, but the full set of differences between the two versions can be obtained through metacpan.

https://metacpan.org/diff/file?source=VPIT/autovivification-0.16&target=VPIT/autovivification-0.18

[haukex]

#!/usr/bin/env perl
use warnings;
use strict;
no autovivification qw{fetch store exists delete}; 

my $h = { a => { p => 2, q => 3 } };

print "perl ver $], autoviv ver $autovivification::VERSION:\n"; 
! $$h{a}{x}{z} and print "a/x/z not\n"; 

__END__

perl ver 5.024004, autoviv ver 0.16:
a/x/z not

perl ver 5.028001, autoviv ver 0.16:
a/x/z not

perl ver 5.024004, autoviv ver 0.18:
Can't vivify reference at a.pl line 9.

perl ver 5.028001, autoviv ver 0.18:
Can't vivify reference at a.pl line 9.

[leszekdubiel]

I've found:

The documentation for the exists operator no longer says that autovivification behaviour "may be fixed in a future release". We've determined that we're not going to change the default behaviour. perl #127712

perl #127712

I understand that there are only two options:

• NO autovivification. Then you can't do if (exists $h{a}{b}{c}{d}) { ... }, because you try to dereference non-existent $h{a}{b}, then you get error.
• Or default (*) behaviour, WITH autovivification, that is when you do if (exists $h{a}{b}{c}{d}) { ... }, then perl will gracefully create $h{a}, $h{a}{b}, $h{a}{b}{c} for you :) :)
(*) -- this is the default behaviour that creators of perl decided not to change

I hoped to find solution that doesn't autovifify when existence is checked, so I could just act like this if (exists $h{a}{b}{c}{d}) { ... } and not like this if (exists $h{a} && exists $h{a}{b} && exists $h{a}{b}{c} && exists $h{a}{b}{c}{d}) { ... }

My preferred default behaviour would be to return undef for $h{a}{b}{c}{d} and NOT create $h{a}, $h{a}{b}, $h{a}{b}{c}... This is not possible.