Filters

• We could use a serialization module like Storable

  • It will convert arbitrary values to strings, and back:

 use Storable;
 $hash{numbers} = freeze [1, 4, 2, 8, 5, 7];

 $aref = thaw $hash{numbers};
 print "@$aref\n";

 1 4 2 8 5 7

• This is kind of a pain

• DB_File will do it automatically:

 my $db = tied %hash;
 $db->filter_store_value(sub { $_ = Storable::freeze($_) });
 $db->filter_fetch_value(sub { $_ = Storable::thaw($_) });

• Now this works:

 $hash{numbers} = [1, 4, 2, 8, 5, 7];
 $aref = $hash{numbers};
 print "@$aref\n";

• freeze and thaw are called automatically

  • Note that the filters use $_ for input and output

• Similarly, filter_store_key and filter_fetch_key