my $package = My::Package->new( \&user_sub );

$package->add_data( @user_data );

my $value = $package->operate_on_all_data();

sub user_sub
{
   # code here
}

##</code><code>##

# in My::Package
sub operater_on_all_data
{
    my $value;
    foreach ( @internal_data_storage ) {
       $value += &user_sub_variable();
    }
}

# in user_sub
sub user_sub {
    return $_ * 2;
}

##</code><code>##

# in My::Package
sub operater_on_all_data
{
    my $value;
    my $i = 0;
    foreach ( @internal_data_storage ) {
       $helper = $i++;
       $value += &user_sub_variable();
    }
}

# in user_sub
sub user_sub {
    return $_ * 2 * $My::Package::helper;
}

##</code><code>##

# in My::Package
sub operater_on_all_data
{
    my $value;
    my $i = 0;
    foreach ( @internal_data_storage ) {
       $helper = $i++;
       $value += &user_sub_variable( $i++ );
    }
}

# in user_sub
sub user_sub {
    my $multiplier = shift;
    return $_ * 2 * $multiplier;
}