Question

I’m finding it very convenient to pass configuration and other data that is read or calculated once but then used many times throughout a program by using Perl’s use mechanism. I’m doing this by exporting a hash into the caller’s namespace. For example:

package Myconfiguration;

my %config;

sub import {
    my $callpkg = caller(0);
    my $expsym = $_[1];

    configure() unless %config;

    *{"$callpkg\::$expsym"} = \%config;
}

and then in other modules:

use MyConfiguration (loc_config_sym);

if ( $loc_config_sym{paramater} ) {
    # ... do stuff ...
}

However, I’m not sure about this as a best practice. Is it better to add a method that returns a hash ref with the data? Something else?

Answer 1

If you only want to read the values of %config, then why not have a routine to do it for you?

 my %config;
 sub config_value
 {
      my ($value) = @_;
      return $config{$value};
 }

You could export this by default if you wanted to:

package Mypackage;
require Exporter;
@EXPORT = qw/config_value/;

The reason that I would not allow access to the hash all over the place in lots of different modules is that I would have a hard time mentally keeping track of all the places it was being used. I would rather make the above kind of access routine so that, if some bug happened, I could add a print statement to the routine, or something, to find out when the value was being accessed. I don’t know if that is related to “best practices” or it is just because I’m stupid, but the kind of confusion created by global variables scares me.

There’s no reason you can’t have a set routine too:

 sub set_value
 {
      my ($key, $value) = @_;
      $config{$key} = $value;
 }