Hi Octavian, On Sun, 7 Aug 2011 12:28:27 +0300 "Octavian Rasnita" <orasn...@gmail.com> wrote:
> Hi, > > I made the following test script: > > use strict; > use warnings FATAL => 'all'; > use LWP::UserAgent; > > my $fields; > > my $ua = LWP::UserAgent->new; > my $res = $ua->get( 'http://www.google.com/', %$fields ); > > This script runs with no errors, although the variable $fields is undefined > and it is used as a hash reference and I don't understand why. > > If I use it in the following line however, it gives the error "Can't use an > undefined value as a HASH reference": my %params = %$fields; > > Does anyone have an explanation why in the first example it works fine? > I've simplified the program to: [CODE] #!/usr/bin/perl use strict; use warnings FATAL => 'all'; my $fields; sub mysub { return; } mysub('hello', %$fields); # my @x = ('hello', %$fields); print("Hello\n"); [/CODE] This is the IRC talk on #p5p about it: [QUOTE] * Now talking on #p5p * Topic for #p5p is: git://perl5.git.perl.org/perl.git | "Well volunteered" * Topic for #p5p set by Nicholas!wlzig6e...@colon.colondot.net at Mon Aug 1 17:37:33 2011 <rindolf> Hi all. From beginners@perl.org, why doesn't this program throw an exception: http://paste.debian.net/125354/ . <dipsy> [ debian Pastezone ] <vincent> autovivification does not warn <rindolf> vincent: how is that autovivification? <vincent> look at $fields at the end <rindolf> vincent: oh, so it creates an empty hash? <rindolf> vincent: but it's OK if I do my @a = (%$fields) - then it warns. <vincent> because in that case %$fields is not a lvavlue <vincent> s,vl,l, <vincent> perl must autovivify when %$fields is passed as an argument, because you could do @_ = (key => $value) in your sub <rindolf> vincent: ah. <vincent> well, it doesn't work. but argument lists are lvalue contexts, so it could be argued that it ought to work that way <rindolf> vincent: OK. <rindolf> vincent: well, it seems like a leaky abstraction and it's another reason why one should use «my ($self, $args) = @_;» instead of «my ($self, %args) = @_;». <rindolf> vincent: thanks for the explanation. <vincent> please don't advocate anything in my name <rindolf> vincent: what? [/QUOTE] Regards, Shlomi Fish -- ----------------------------------------------------------------- Shlomi Fish http://www.shlomifish.org/ Optimising Code for Speed - http://shlom.in/optimise The X in XSLT stands for eXtermination. Please reply to list if it's a mailing list post - http://shlom.in/reply . -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
