http://qs321.pair.com?node_id=541361


in reply to eval a reference to a my hash

I don't understand why this doesn't work, but I do have a suggestion about how to fix it. Instead of using seperate hashes with different names, have a hash of hashrefs. Then you don't need an eval STRING or symbolic references to make it work.

Warning: Unless otherwise stated, code is untested. Do not use without understanding. Code is posted in the hopes it is useful, but without warranty. All copyrights are relinquished into the public domain unless otherwise stated. I am not an angel. I am capable of error, and err on a fairly regular basis. If I made a mistake, please let me know (such as by replying to this node).

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Re^2: eval a reference to a my hash
by cdarke (Prior) on Apr 05, 2006 at 12:37 UTC
    Nice solution, I wanted to get rid of the eval anyway. Thanks!
    I would still love to know why the original doesn't work.
[reply]

      By the time the eval STRING code runs, lexicals don't really have names anymore, so Perl can't look them up by name.

[reply]
        And that explains why making them our variables fixes the problem. Many thanks (I'm using an extra hash now and got rid of the eval, but it is worth knowing).
        Cheers
[reply]
      When you say the original doesn't work, what makes you think it isn't?

      It seems your simplified fragment is not demonstrating the problem, because: 

      #!/usr/bin/perl -w
                                                                      
+          
# Strict
use strict;
use warnings;
                                                                      
+          
# Libraries
use Carp;
use Data::Dumper;
                                                                      
+          
                                                                      
+          
my %drink;
# other attribute hashes
                                                                      
+          
set('larry', 'drink', 'Old Speckled Hen');
print $drink{'larry'}, "\n";
# print "Dump(\%drink) => [%s]\n", Dumper(\%drink);
                                                                      
+          
                                                                      
+          
sub set {
   my ($key, $attr, $value) = @_;
                                                                      
+          
   my $hashref;
   eval "\$hashref = \\\%$attr";
                                                                      
+          
   if ( !defined $hashref ) {
      carp 'Invalid attribute name';
   }
   else {
      $hashref->{$key} = $value;
   }
}

      [download]
      is working for me: 
      % prog541345.pl
Old Speckled Hen

      [download]
      If that isn't what you're getting, please compare the above code fragment (based on what you provided in your post) to your actual code, and see if that helps locate the problem.
      s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/
[reply]
[d/l]
[select]
        It works because of the print statement. Take that out and it will fail. Thanks anyway.
[reply]

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