hash "member" of a module

npc has asked for the wisdom of the Perl Monks concerning the following question:

I'm trying to create a module that has a hashref as a data member. It appears to function correctly in the same method its initialized in (new) but when I reference it later in another function (test) I get "is not a HASH ref." In the test() method, if I Data::Dumper($self), I can see the hash inside(data), but I can't access $self->{data} directly. here is the module:

package Foo;

use strict;

use Data::Dumper;
use Exporter;

our ($VERSION,@ISA,@EXPORT,@EXPORT_OK);
$VERSION     = 0.99;
@ISA         = qw(Exporter);
@EXPORT      = @EXPORT_OK;
@EXPORT_OK   = qw(new test);

sub new(){
  my $self = {};
  $self->{data} = {};
  $self->{data}->{start_url} = "https://www.w.com/home.html";

  bless \$self;
}

sub test(){
  my $self = shift;
#  print $self->{data}->{start_url};
#  print Dumper($self);
  print Dumper($self->{data});
}
[download]

and here is the simple test program:

use strict;
use warnings;
use Foo;

my $obj = Foo->new();
$obj->test();
[download]

and here is the error: Not a HASH reference at Foo.pm line 26.

Comment on hash "member" of a module Select or Download Code

Replies are listed 'Best First'.
Re: hash "member" of a module by Corion (Patriarch) on Apr 15, 2009 at 18:06 UTC
`bless \$self;` [download] Here, you're blessing a reference to a hash reference. You want to bless the hash reference instead: `bless $self;` [download] Also, you will likely want to make your class subclassable, so use the two-argument form of bless: `sub new { my ($class) = @_; my $self = {}; $self->{data} = {}; $self->{data}->{start_url} = "https://www.w.com/home.html"; bless $self, $class; }` [download] Also, I've removed the parentheses from the subroutine declaration, as methods ignore any declared prototypes.	[reply] [d/l] [select]
Re: hash "member" of a module by kennethk (Abbot) on Apr 15, 2009 at 18:07 UTC
That's because you are not returning a hash reference from your function. Within new, $self is a hash reference. When you return \$self, you return a reference to the hash reference, which is a scalar reference. See perlref or perlreftut. The following code works. `package Foo; use strict; use Data::Dumper; use Exporter; our ($VERSION,@ISA,@EXPORT,@EXPORT_OK); $VERSION = 0.99; @ISA = qw(Exporter); @EXPORT = @EXPORT_OK; @EXPORT_OK = qw(new test); sub new(){ my $self = {}; $self->{data} = {}; $self->{data}->{start_url} = "https://www.w.com/home.html"; bless $self; } sub test(){ my $self = shift; # print $self->{data}->{start_url}; # print Dumper($self); print Dumper($self->{data}); }` [download] and `use strict; use warnings; use Foo; my $obj = Foo->new(); $obj->test();` [download]	[reply] [d/l] [select]
Re^2: hash "member" of a module by npc (Initiate) on Apr 15, 2009 at 18:12 UTC
How silly of me, thank you monks.	[reply]