module reference is used in a confusing way

[gwhite]

Going through some code someone else wrote and found this and I don't understand it. Can someone shed some light?

#this creates a new $config thing
my $config = new ConfigReader::Simple($config_file);
#this checks for a true in one of the elements of the $config
if ($config->adv_conf){
...
}
#this creates an array out of a list of words
my @batch_list = split /\s+/, $config->batch_list;
#the next line puts a reference to the array into the $config
#but why the $$ and no ->
$$config{batch_list} = \@batch_list;
#could it be done just as easily with this
$config->set(batch_list, \@batch_list);
#I am thinking probably not since the doc says:
#set( DIRECTIVE, VALUE ) 
#Sets the value for DIRECTIVE to VALUE. The DIRECTIVE need not already
+ exist. This overwrites previous values.
#The VALUE must be a simple scalar. It cannot be a reference. If the V
+ALUE is a reference, the function prints a warning and returns false.

and what are the proper ways to access that $config element?
my @list = @{$$config{batch_list}};
my @list = @{$config->batch_list};

[kennethk]

$$config{batch_list} = \@batch_list

This stores a reference to the @batch_list array in the 'batch_list' element of an anonymous hash. The reference to the anonymous hash is stored in $config. If you want to access the stored array, it can be read as

my @list = @{$$config{batch_list}}

or

my @list = @{$config->{batch_list}}

as well, I'm sure, as a half dozen other ways.