Comments on: Autovivification bit me today

By: Jeremy Leader

Jeremy Leader — Tue, 07 Dec 2010 23:44:30 +0000

What happens if you’ve already called load_hashref earlier, and it loaded an empty hash? Should you call load_hashref again this time around, or not?

I think that argues for guarding against autovivification, and in favor of distinguishing between 2 different states:

$hashref is defined: means load_hashref has already been called, even if it loaded 0 keys

$hashref is not defined: means load_hashref hasn’t been called yet.

By: Aristotle Pagaltzis

Aristotle Pagaltzis — Sun, 21 Nov 2010 23:09:22 +0000

Even if you stick with keys, you don’t need scalar. But I would add a clause to prevent autovivification instead of permitting an empty hash. Note that a normal reference can never be a false value, so you don’t really need defined, just checking for truthiness is fine. Bottom line, I’d write:


return if $hashref and $hashref->{something};
load_hashref $hashref if not $hashref;

By: b

Thu, 28 May 2009 01:06:40 +0000

I like

return if $hashref and exists $hashref->{something};

much better than counting the keys.

By: lwsitu

lwsitu — Wed, 27 May 2009 23:44:57 +0000

you don’t need to use scalar keys, just using a hash in scalar context would work as well

By: Laufeyjarson

Laufeyjarson — Wed, 27 May 2009 20:55:58 +0000

I was following the advice from http://www.perlmonks.org/?node_id=173677 which points out that not all tied hashes behave properly in those situations.

In my specific case, it would have been fine, but in the general case it might not always work.

By: matt

matt — Wed, 27 May 2009 15:10:44 +0000

you shouldn’t need scalar keys
my $hashref = {};
return if exists $hashref->{something};
load_hashref($hashref) unless %$hashref;

By: Pedro Melo

Pedro Melo — Wed, 27 May 2009 06:42:25 +0000

The last line can even be simpler:

load_hashref($hashref) unless %$hashref;

Best regards,