wfsp has asked for the wisdom of the Perl Monks concerning the following question:

Does this eliminate a global? Or does it just give the same problem a fancy hat? 
package my::data;

use strict;
use warnings;

my $Config ={
# this would be loaded from a config.ini file
  root => {
    local => 'c:/local',
    remote => 'docroot',
  },
  category => {
    europe => 'europe.html',
    women  => 'women.html',
  },
};

sub Config{
  if (@_ == 4){
    $Config->{$_[1]}{$_[2]} = $_[3];
    return $_[3];
  }
  elsif (@_ == 3){
    if (exists $Config->{$_[1]}{$_[2]}){
      return $Config->{$_[1]}{$_[2]};
    }
    else{
      return;
    }
  }
  else{
    return;
  }
}

1;

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After adding 
use my::data;

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to any module $Config can then be accessed: 
$data = my::data->Config('root', 'local');

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or changed: 
my::data->Config('root', 'local' => 'c:/local_path');

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Is this "a way to do it"? Or is it just madness?

Replies are listed 'Best First'.
Re: Using "Class Data as Package Variables" to hold a global
by salva (Canon) on Apr 30, 2005 at 15:07 UTC
    Does this eliminate a global?

    No, it's just a new hat, but on the other hand, there is nothing wrong on using globals for storing global data and for most apps, configuration data is just global data.

    Anyway, I would break the configuration module in two:
    a) a generic class abstracting the configuration access logic.
    b) a module implementing a singleton to access the global configuration specific to the app.

    For example:

    class Config::Foo; 

    package Config::Foo;

sub new {
  my $class = shift;
  my $fn = shift;
  ## read the configuration file here
  ## ...
  bless $this, $class 
}

sub get {
  my $this=shift;
  my $key=shift;
  my $default=shift;
  exists $this->{$key} ? $this->{$key} : $default;
}

sub set {
  my $this=shift;
  my $key=shift;
  my $value=shift;
  $this->{$key}=$value;
}

1;

---

package MyApp::Config;

use Config::Foo;
require Exporter;
our @EXPORT=qw(config);
our @ISA=qw(Exporter);   ## (updated!)

my $config;

sub config {
  $config=Config::Foo->new('/etc/myapp.conf')
    unless defined $config;
  $config;
}

1;

---
# and in your app

use MyApp::Config;

my $foo=config->get(foo);
config->set(bar => 'new_bar');

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[d/l]
      class Config::Foo;

      You had me searching perlfunc there...class? Never seen that before in Perl ;-) I take it you meant package?

      Remember rule one...
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[d/l]
        oops, sorry, yes, I meant package!
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      salva

      Many thanks. I've had a slight snag with the syntax. If I uncomment the line in the following code I get:

      Can't locate object method "set" via package "config" (perhaps you forgot to load "config"?) at myapp.pl line 9.
      #!/usr/bin/perl

use strict;
use warnings;

use Auto::Config;

my $root_local = Auto::Config::config->get(root => 'local');

# This line produces the error message
# config->set('root', remote => 'docroot_new');

Auto::Config::config->set('root', remote => 'docroot_new');

print "$root_local\n";

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      Do the methods have to be fully qualified like that? Or, more likely, have I goofed?

      Read more... (1275 Bytes)
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[d/l]
[select]
        I had forgotten to set @ISA, check me original post, I have updated it!
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Re: Using "Class Data as Package Variables" to hold a global
by brian_d_foy (Abbot) on Apr 30, 2005 at 17:21 UTC

    By scoping the variable to the file (or class), it's no longer global. Only things in that same file can access it. Some situations can naturally use a file scoped lexical variable: it's the same argument as class versus instance data in other languages.

    Good luck :)

    --
    brian d foy <brian@stonehenge.com>
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