Re: autovivication gonna make me lose my mind

If you're dereferencing an element as an lvalue (i.e., in a kind of assignment), it will autovivify. If you're dereferencing otherwise, it will fail.

For example:

$ perl -le 'use strict;my %h;push @{$h{first}}, "hello";print $h{first
+}'
ARRAY(0x8153d78)
$ perl -e 'use strict;my %h;print @{$h{first}}, "hello";'
Can't use an undefined value as an ARRAY reference at -e line 1.
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Re^2: autovivication gonna make me lose my mind by dreadpiratepeter (Priest) on Sep 16, 2008 at 16:06 UTC
A ha, that's my disconnect. I got the error for an rvalue at some point and drew the wrong conclusion (I generalized it to lvalues too). So I have cargo-culted myself for the last few years. Time to simplify some code. Thank you so much for dispelling my confusion -pete "Worry is like a rocking chair. It gives you something to do, but it doesn't get you anywhere."	[reply]
Re^2: autovivication gonna make me lose my mind by ig (Vicar) on Nov 04, 2008 at 14:06 UTC
I think autovivification can happen in contexts other than dereferencing an element as an lvalue. Consider the following script. `#!/usr/bin/perl use strict; use warnings; use Data::Dumper; my $hashref; print "exists\n" if(exists($hashref->{foo}->{bar})); print Dumper($hashref);` [download] It prints `$VAR1 = { 'foo' => {} };` [download] So, unless the argument to exists is dereferenced as an lvalue (I don't know how it is implemented) there are other contexts. Explaining Autovivication, Accidentally creating hash elements with grep { defined } on a hash slice and The Bad, the Ugly, and the Good of autovivification have more info.	[reply] [d/l] [select]