In the CPAN docs it, the calls it init() without any arguments. Try replacing

Gtk2->init(\@ARGV);
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with

Gtk2->init();
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Update: when calling a PACKAGE->method(), the class is passed as the first argument automatically. So that is where Usage: init(class) comes in.

Example:

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

Tom->init;

package Tom;
sub init(){
  print "Calling init\n";
  print "$_\n" for(@_);
}

__OUTPUT__
Calling init
Tom
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