use warnings;
use strict;

package Config {
	sub new {
		my ($class,%args) = @_;
		my $self = {};
		# code to read $args{config_file} into $self
		return bless $self, $class;
	}
}

package Object {
	sub new {
		my ($class,%args) = @_;
		my $self = _parse_data_with_config($args{config},$args{data});
		return bless $self, $class;
	}
	sub _parse_data_with_config {
		my ($config, $data) = @_;
		my $self = {};
		# complex code to build $self from $data using $config
		return $self;
	}
	# ...
}

my $config = Config->new( config_file => "file.xml" );
my $obj1 = Object->new( config => $config, data => { foo=>123 } );
my $obj2 = Object->new( config => $config, data => { bar=>456 } );