PERL :: An Object Accesses its own Attributes in Another Method-CodePudding

Perl newbie here. I've been Googling for hours on what I thought would be a relatively simple problem. Suppose I have this code:

#!/usr/bin/perl
use warnings;
use strict;

package Guy;
sub new {
        my $type = shift;
        my %params = @_;
        my $self = {};
        $self->{'First'} = $params{'First'};
        $self->{'Middle'} = $params{'Middle'};
        $self->{'Last'} = $params{'Last'};
        bless $self, $type;
}
sub printMe
{
        printf "-----------------------------------\n";
        printf "My type is: \"$self->{type}\"\n";        # Line 18
        printf "First  ::  $self->{First}\n";            # Line 19
        printf "Middle ::  $self->{Middle}\n";           # Line 20
        printf "Last   ::  $self->{Last}\n";             # Line 21
        printf "-----------------------------------\n";
}

package main;
my $dude = Guy->new( 'First' => "John", 'Middle' => "Jacob", 'Last' => "Smith" );
$dude->printMe();

Output is:

me@ubuntu1$ ./toy01.perl
Global symbol "$self" requires explicit package name (did you forget to declare "my $self"?) at ./toy01.perl line 18.
Global symbol "$self" requires explicit package name (did you forget to declare "my $self"?) at ./toy01.perl line 19.
Global symbol "$self" requires explicit package name (did you forget to declare "my $self"?) at ./toy01.perl line 20.
Global symbol "$self" requires explicit package name (did you forget to declare "my $self"?) at ./toy01.perl line 21.
Execution of ./toy01.perl aborted due to compilation errors.
me@ubuntu1$

So the problem here is that class method printMe() can't access attributes stored in the $self hash, which is populated in the constructor. I'm so confused as to why.

In the constructor, $self is created as a hash, used to store the attributed passed into the constructor. Is $self created with a local scope when it needs to be global, or something like that? Or do I lack a command at the top of the printMe() method that makes $self visible, or something?

And how to refer to attribute type, which is an attribute that is set in the constructor but not stored in the $self hash? (My $self->{type} call is obviously a desperate attempt to stumble upon the solution here.) Any advice or feedback is appreciated here, thank you.

CodePudding user response：

The object is sent to the method as the first parameter, but you need to populate the variable yourself:

sub printMe
{
    my ($self) = @_;
    ...

Note that $self->{type} doesn't exist. Use ref $self or blessed($self) from Scalar::Util.

Also, using printf without a format string is useless. Use print or say instead, or use printf properly:

printf "First  ::  %s\n", $self->{First};