in reply to Whither the truth of a tied hash?

I put together this quick test and it seems to work as expected (I'm using perl : 5.005_02) 
#!/usr/bin/perl -w

 use Fcntl;
 use SDBM_File;

 my %db;
 tie (%db, 'SDBM_File', './t.db', O_RDWR | O_CREAT, 0666);

 my $s=scalar keys (%db);
 print "s=$s\n";
 $db{39485}=1;
 $db{354345}=1;

 $s=scalar keys (%db);
 print "s=$s\n";
 foreach (keys %db){
  print "  \"$_\"\n";
 }
 untie %db;

[download]
producing the following output 
s=0
s=2
  "39485"
  "354345"
What are you tying to? Maybe there's a problem there.


Les Howard
www.lesandchris.com
Author of Net::Syslog and Number::Spell

Replies are listed 'Best First'.
RE: Re: Whither the truth of a tied hash?
by mojotoad (Monsignor) on Apr 28, 2000 at 23:48 UTC
    Your results are the scalar context of keys(). I'm talking about something like the following statement: 
       if (%h) {
      ...do something with a non-empty hash
   }

    As far as I can tell, there is no method in the tied hash class that is invoked for this. Try the following module to test: 

    package TieTest;

use strict;
use Carp;

use vars qw(@ISA);

use Tie::Hash;
@ISA = qw( Tie::StdHash );

sub STORE    { notify('STORE');    shift->SUPER::STORE(@_);    }
sub FETCH    { notify('FETCH');    shift->SUPER::FETCH(@_);    }
sub FIRSTKEY { notify('FIRSTKEY'); shift->SUPER::FIRSTKEY(@_); }
sub NEXTKEY  { notify('NEXTKEY');  shift->SUPER::NEXTKEY(@_);  }
sub EXISTS   { notify('EXISTS');   shift->SUPER::EXISTS(@_);   }
sub DELETE   { notify('DELETE');   shift->SUPER::DELETE(@_);   }
sub CLEAR    { notify('CLEAR');    shift->SUPER::CLEAR(@_);    }

sub notify { print shift, " here.\n"; }

1;
    You can use it with something like this: 
       #!/usr/bin/perl
   use TieTest;
   tie %h, 'TieTest';
   grep($h{$_} = $_, 0 .. 9);
   print "Scalar test:\n";
   $c = %h;
   print "count is $c\n";
    Any ideas?
[reply]
      The only thing I found that helped at all was copying the hash with a simple: 
      my %i = %h;
my $c = %i;
print "count is $c\n";

      [download]
      I even made an AUTOLOAD subroutine, to see if I could trap any other method calls. No luck.
[reply]
[d/l]
        Ah, well. I figured as much. I guess I'll mine the net to see if it's a known problem with perl; if it has not been discussed yet I'll toss it at the porters.
[reply]

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