Hi, Monks: I used to use c++, but beginner for perl. I want to create a singleten class with a bunch of attributes and methods but didn't know how.

 
use strict;
use warnings;

    package MyConfig;
    use XML::Simple;
    my $singleton;
    my $XMLfile_name="";
    my @hostList = ();

    sub new {
        my $class = shift;
        #create singleton
        $singleton ||= bless {}, $class;
#Error here: Useless use of hash element in void context
    $singleton->{$XMLfile_name}=$_[0];
    return $singleton;
    }

    sub loadConfig{
    my $self=shift;
    my $xml = XML::Simple->new;
    my $config = $xml->XMLin($file_name, 
ForceArray => [ 'host', 'component' ]) or die$!;

    my $index=0;
    while($config->{host}->{component}->[$index++])
    {
 push @hostList, $config->{host}->{component}->[0]->{component_name};
    }
   }
1;
[download]

The XML structure is like:

 
<root>
        <component component_name="n1" />
        <component component_name="n2" />
        <component component_name="n3" />
    </root>
[download]

I call code as:

use strict;
use MyConfig;
my $CONFIG = "somefile.xml";
&main;
sub main
{
    my configReader = MyConfig->new( $CONFIG );
    configReader->loadConfig;
}
[download]

As you see, I didn't know how to create and use what we say member variable in c++. The $XMLfile_name and the @hostList here is using as member variables. @hostList used for holding results parsed from the XML file.

Another question: In the new method, as I read package method always put the invoker as the first argument. I suppose 'invoker' for new() means the class MyConfig and return an instance after blessed; And the 'invoker' for loadConfig seems change to be an instance, seems the $self by te first default argument is an instance not the class any more. But as I know the 'new' is an ordinary method as others, not a keywords, why they behaves different?

The last question:I don't think I made my while condition correct. How can I deal with the while index simply using $_? Thanks a lot in advance!!

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