MirOS Manual: perldsc(1)


PERLDSC(1)      Perl Programmers Reference Guide       PERLDSC(1)

NAME

     perldsc - Perl Data Structures Cookbook

DESCRIPTION

     The single feature most sorely lacking in the Perl program-
     ming language prior to its 5.0 release was complex data
     structures.  Even without direct language support, some
     valiant programmers did manage to emulate them, but it was
     hard work and not for the faint of heart.  You could occa-
     sionally get away with the $m{$AoA,$b} notation borrowed
     from awk in which the keys are actually more like a single
     concatenated string "$AoA$b", but traversal and sorting were
     difficult.  More desperate programmers even hacked Perl's
     internal symbol table directly, a strategy that proved hard
     to develop and maintain--to put it mildly.

     The 5.0 release of Perl let us have complex data structures.
     You may now write something like this and all of a sudden,
     you'd have an array with three dimensions!

         for $x (1 .. 10) {
             for $y (1 .. 10) {
                 for $z (1 .. 10) {
                     $AoA[$x][$y][$z] =
                         $x ** $y + $z;
                 }
             }
         }

     Alas, however simple this may appear, underneath it's a much
     more elaborate construct than meets the eye!

     How do you print it out?  Why can't you say just "print
     @AoA"?  How do you sort it?  How can you pass it to a func-
     tion or get one of these back from a function?  Is it an
     object?  Can you save it to disk to read back later?  How do
     you access whole rows or columns of that matrix?  Do all the
     values have to be numeric?

     As you see, it's quite easy to become confused.  While some
     small portion of the blame for this can be attributed to the
     reference-based implementation, it's really more due to a
     lack of existing documentation with examples designed for
     the beginner.

     This document is meant to be a detailed but understandable
     treatment of the many different sorts of data structures you
     might want to develop.  It should also serve as a cookbook
     of examples.  That way, when you need to create one of these
     complex data structures, you can just pinch, pilfer, or pur-
     loin a drop-in example from here.

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     Let's look at each of these possible constructs in detail.
     There are separate sections on each of the following:

     * arrays of arrays
     * hashes of arrays
     * arrays of hashes
     * hashes of hashes
     * more elaborate constructs

     But for now, let's look at general issues common to all
     these types of data structures.

REFERENCES

     The most important thing to understand about all data struc-
     tures in Perl -- including multidimensional arrays--is that
     even though they might appear otherwise, Perl @ARRAYs and
     %HASHes are all internally one-dimensional.  They can hold
     only scalar values (meaning a string, number, or a refer-
     ence).  They cannot directly contain other arrays or hashes,
     but instead contain references to other arrays or hashes.

     You can't use a reference to an array or hash in quite the
     same way that you would a real array or hash.  For C or C++
     programmers unused to distinguishing between arrays and
     pointers to the same, this can be confusing.  If so, just
     think of it as the difference between a structure and a
     pointer to a structure.

     You can (and should) read more about references in the
     perlref(1) man page.  Briefly, references are rather like
     pointers that know what they point to.  (Objects are also a
     kind of reference, but we won't be needing them right
     away--if ever.)  This means that when you have something
     which looks to you like an access to a two-or-more-
     dimensional array and/or hash, what's really going on is
     that the base type is merely a one-dimensional entity that
     contains references to the next level.  It's just that you
     can use it as though it were a two-dimensional one.  This is
     actually the way almost all C multidimensional arrays work
     as well.

         $array[7][12]                       # array of arrays
         $array[7]{string}                   # array of hashes
         $hash{string}[7]                    # hash of arrays
         $hash{string}{'another string'}     # hash of hashes

     Now, because the top level contains only references, if you
     try to print out your array in with a simple print() func-
     tion, you'll get something that doesn't look very nice, like
     this:

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         @AoA = ( [2, 3], [4, 5, 7], [0] );
         print $AoA[1][2];
       7
         print @AoA;
       ARRAY(0x83c38)ARRAY(0x8b194)ARRAY(0x8b1d0)

     That's because Perl doesn't (ever) implicitly dereference
     your variables. If you want to get at the thing a reference
     is referring to, then you have to do this yourself using
     either prefix typing indicators, like "${$blah}",
     "@{$blah}", "@{$blah[$i]}", or else postfix pointer arrows,
     like "$a->[3]", "$h->{fred}", or even "$ob->method()->[3]".

COMMON MISTAKES

     The two most common mistakes made in constructing something
     like an array of arrays is either accidentally counting the
     number of elements or else taking a reference to the same
     memory location repeatedly.  Here's the case where you just
     get the count instead of a nested array:

         for $i (1..10) {
             @array = somefunc($i);
             $AoA[$i] = @array;      # WRONG!
         }

     That's just the simple case of assigning an array to a
     scalar and getting its element count.  If that's what you
     really and truly want, then you might do well to consider
     being a tad more explicit about it, like this:

         for $i (1..10) {
             @array = somefunc($i);
             $counts[$i] = scalar @array;
         }

     Here's the case of taking a reference to the same memory
     location again and again:

         for $i (1..10) {
             @array = somefunc($i);
             $AoA[$i] = \@array;     # WRONG!
         }

     So, what's the big problem with that?  It looks right,
     doesn't it? After all, I just told you that you need an
     array of references, so by golly, you've made me one!

     Unfortunately, while this is true, it's still broken.  All
     the references in @AoA refer to the very same place, and
     they will therefore all hold whatever was last in @array!
     It's similar to the problem demonstrated in the following C
     program:

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         #include <pwd.h>
         main() {
             struct passwd *getpwnam(), *rp, *dp;
             rp = getpwnam("root");
             dp = getpwnam("daemon");

             printf("daemon name is %s\nroot name is %s\n",
                     dp->pw_name, rp->pw_name);
         }

     Which will print

         daemon name is daemon
         root name is daemon

     The problem is that both "rp" and "dp" are pointers to the
     same location in memory!  In C, you'd have to remember to
     malloc() yourself some new memory.  In Perl, you'll want to
     use the array constructor "[]" or the hash constructor "{}"
     instead.   Here's the right way to do the preceding broken
     code fragments:

         for $i (1..10) {
             @array = somefunc($i);
             $AoA[$i] = [ @array ];
         }

     The square brackets make a reference to a new array with a
     copy of what's in @array at the time of the assignment.
     This is what you want.

     Note that this will produce something similar, but it's much
     harder to read:

         for $i (1..10) {
             @array = 0 .. $i;
             @{$AoA[$i]} = @array;
         }

     Is it the same?  Well, maybe so--and maybe not.  The subtle
     difference is that when you assign something in square
     brackets, you know for sure it's always a brand new refer-
     ence with a new copy of the data. Something else could be
     going on in this new case with the "@{$AoA[$i]}}" derefer-
     ence on the left-hand-side of the assignment.  It all
     depends on whether $AoA[$i] had been undefined to start
     with, or whether it already contained a reference.  If you
     had already populated @AoA with references, as in

         $AoA[3] = \@another_array;

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     Then the assignment with the indirection on the left-hand-
     side would use the existing reference that was already
     there:

         @{$AoA[3]} = @array;

     Of course, this would have the "interesting" effect of
     clobbering @another_array.  (Have you ever noticed how when
     a programmer says something is "interesting", that rather
     than meaning "intriguing", they're disturbingly more apt to
     mean that it's "annoying", "difficult", or both?  :-)

     So just remember always to use the array or hash construc-
     tors with "[]" or "{}", and you'll be fine, although it's
     not always optimally efficient.

     Surprisingly, the following dangerous-looking construct will
     actually work out fine:

         for $i (1..10) {
             my @array = somefunc($i);
             $AoA[$i] = \@array;
         }

     That's because my() is more of a run-time statement than it
     is a compile-time declaration per se.  This means that the
     my() variable is remade afresh each time through the loop.
     So even though it looks as though you stored the same vari-
     able reference each time, you actually did not!  This is a
     subtle distinction that can produce more efficient code at
     the risk of misleading all but the most experienced of pro-
     grammers.  So I usually advise against teaching it to
     beginners.  In fact, except for passing arguments to func-
     tions, I seldom like to see the gimme-a-reference operator
     (backslash) used much at all in code.  Instead, I advise
     beginners that they (and most of the rest of us) should try
     to use the much more easily understood constructors "[]" and
     "{}" instead of relying upon lexical (or dynamic) scoping
     and hidden reference-counting to do the right thing behind
     the scenes.

     In summary:

         $AoA[$i] = [ @array ];      # usually best
         $AoA[$i] = \@array;         # perilous; just how my() was that array?
         @{ $AoA[$i] } = @array;     # way too tricky for most programmers

CAVEAT ON PRECEDENCE

     Speaking of things like "@{$AoA[$i]}", the following are
     actually the same thing:

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         $aref->[2][2]       # clear
         $$aref[2][2]        # confusing

     That's because Perl's precedence rules on its five prefix
     dereferencers (which look like someone swearing: "$ @ * %
     &") make them bind more tightly than the postfix subscript-
     ing brackets or braces!  This will no doubt come as a great
     shock to the C or C++ programmer, who is quite accustomed to
     using *a[i] to mean what's pointed to by the i'th element of
     "a".  That is, they first take the subscript, and only then
     dereference the thing at that subscript.  That's fine in C,
     but this isn't C.

     The seemingly equivalent construct in Perl, $$aref[$i] first
     does the deref of $aref, making it take $aref as a reference
     to an array, and then dereference that, and finally tell you
     the i'th value of the array pointed to by $AoA. If you
     wanted the C notion, you'd have to write "${$AoA[$i]}" to
     force the $AoA[$i] to get evaluated first before the leading
     "$" dereferencer.

WHY YOU SHOULD ALWAYS "use strict"
     If this is starting to sound scarier than it's worth, relax.
     Perl has some features to help you avoid its most common
     pitfalls.  The best way to avoid getting confused is to
     start every program like this:

         #!/usr/bin/perl -w
         use strict;

     This way, you'll be forced to declare all your variables
     with my() and also disallow accidental "symbolic dereferenc-
     ing".  Therefore if you'd done this:

         my $aref = [
             [ "fred", "barney", "pebbles", "bambam", "dino", ],
             [ "homer", "bart", "marge", "maggie", ],
             [ "george", "jane", "elroy", "judy", ],
         ];

         print $aref[2][2];

     The compiler would immediately flag that as an error at com-
     pile time, because you were accidentally accessing @aref, an
     undeclared variable, and it would thereby remind you to
     write instead:

         print $aref->[2][2]

DEBUGGING

     Before version 5.002, the standard Perl debugger didn't do a
     very nice job of printing out complex data structures.  With

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     5.002 or above, the debugger includes several new features,
     including command line editing as well as the "x" command to
     dump out complex data structures.  For example, given the
     assignment to $AoA above, here's the debugger output:

         DB<1> x $AoA
         $AoA = ARRAY(0x13b5a0)
            0  ARRAY(0x1f0a24)
               0  'fred'
               1  'barney'
               2  'pebbles'
               3  'bambam'
               4  'dino'
            1  ARRAY(0x13b558)
               0  'homer'
               1  'bart'
               2  'marge'
               3  'maggie'
            2  ARRAY(0x13b540)
               0  'george'
               1  'jane'
               2  'elroy'
               3  'judy'

CODE EXAMPLES

     Presented with little comment (these will get their own man-
     pages someday) here are short code examples illustrating
     access of various types of data structures.

ARRAYS OF ARRAYS

     Declaration of an ARRAY OF ARRAYS

      @AoA = (
             [ "fred", "barney" ],
             [ "george", "jane", "elroy" ],
             [ "homer", "marge", "bart" ],
           );

     Generation of an ARRAY OF ARRAYS

      # reading from file
      while ( <> ) {
          push @AoA, [ split ];
      }

      # calling a function
      for $i ( 1 .. 10 ) {
          $AoA[$i] = [ somefunc($i) ];
      }

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      # using temp vars
      for $i ( 1 .. 10 ) {
          @tmp = somefunc($i);
          $AoA[$i] = [ @tmp ];
      }

      # add to an existing row
      push @{ $AoA[0] }, "wilma", "betty";

     Access and Printing of an ARRAY OF ARRAYS

      # one element
      $AoA[0][0] = "Fred";

      # another element
      $AoA[1][1] =~ s/(\w)/\u$1/;

      # print the whole thing with refs
      for $aref ( @AoA ) {
          print "\t [ @$aref ],\n";
      }

      # print the whole thing with indices
      for $i ( 0 .. $#AoA ) {
          print "\t [ @{$AoA[$i]} ],\n";
      }

      # print the whole thing one at a time
      for $i ( 0 .. $#AoA ) {
          for $j ( 0 .. $#{ $AoA[$i] } ) {
              print "elt $i $j is $AoA[$i][$j]\n";
          }
      }

HASHES OF ARRAYS

     Declaration of a HASH OF ARRAYS

      %HoA = (
             flintstones        => [ "fred", "barney" ],
             jetsons            => [ "george", "jane", "elroy" ],
             simpsons           => [ "homer", "marge", "bart" ],
           );

     Generation of a HASH OF ARRAYS

      # reading from file
      # flintstones: fred barney wilma dino
      while ( <> ) {
          next unless s/^(.*?):\s*//;
          $HoA{$1} = [ split ];
      }

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      # reading from file; more temps
      # flintstones: fred barney wilma dino
      while ( $line = <> ) {
          ($who, $rest) = split /:\s*/, $line, 2;
          @fields = split ' ', $rest;
          $HoA{$who} = [ @fields ];
      }

      # calling a function that returns a list
      for $group ( "simpsons", "jetsons", "flintstones" ) {
          $HoA{$group} = [ get_family($group) ];
      }

      # likewise, but using temps
      for $group ( "simpsons", "jetsons", "flintstones" ) {
          @members = get_family($group);
          $HoA{$group} = [ @members ];
      }

      # append new members to an existing family
      push @{ $HoA{"flintstones"} }, "wilma", "betty";

     Access and Printing of a HASH OF ARRAYS

      # one element
      $HoA{flintstones}[0] = "Fred";

      # another element
      $HoA{simpsons}[1] =~ s/(\w)/\u$1/;

      # print the whole thing
      foreach $family ( keys %HoA ) {
          print "$family: @{ $HoA{$family} }\n"
      }

      # print the whole thing with indices
      foreach $family ( keys %HoA ) {
          print "family: ";
          foreach $i ( 0 .. $#{ $HoA{$family} } ) {
              print " $i = $HoA{$family}[$i]";
          }
          print "\n";
      }

      # print the whole thing sorted by number of members
      foreach $family ( sort { @{$HoA{$b}} <=> @{$HoA{$a}} } keys %HoA ) {
          print "$family: @{ $HoA{$family} }\n"
      }

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      # print the whole thing sorted by number of members and name
      foreach $family ( sort {
                                 @{$HoA{$b}} <=> @{$HoA{$a}}
                                             ||
                                         $a cmp $b
                 } keys %HoA )
      {
          print "$family: ", join(", ", sort @{ $HoA{$family} }), "\n";
      }

ARRAYS OF HASHES

     Declaration of an ARRAY OF HASHES

      @AoH = (
             {
                 Lead     => "fred",
                 Friend   => "barney",
             },
             {
                 Lead     => "george",
                 Wife     => "jane",
                 Son      => "elroy",
             },
             {
                 Lead     => "homer",
                 Wife     => "marge",
                 Son      => "bart",
             }
       );

     Generation of an ARRAY OF HASHES

      # reading from file
      # format: LEAD=fred FRIEND=barney
      while ( <> ) {
          $rec = {};
          for $field ( split ) {
              ($key, $value) = split /=/, $field;
              $rec->{$key} = $value;
          }
          push @AoH, $rec;
      }

      # reading from file
      # format: LEAD=fred FRIEND=barney
      # no temp
      while ( <> ) {
          push @AoH, { split /[\s+=]/ };
      }

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      # calling a function  that returns a key/value pair list, like
      # "lead","fred","daughter","pebbles"
      while ( %fields = getnextpairset() ) {
          push @AoH, { %fields };
      }

      # likewise, but using no temp vars
      while (<>) {
          push @AoH, { parsepairs($_) };
      }

      # add key/value to an element
      $AoH[0]{pet} = "dino";
      $AoH[2]{pet} = "santa's little helper";

     Access and Printing of an ARRAY OF HASHES

      # one element
      $AoH[0]{lead} = "fred";

      # another element
      $AoH[1]{lead} =~ s/(\w)/\u$1/;

      # print the whole thing with refs
      for $href ( @AoH ) {
          print "{ ";
          for $role ( keys %$href ) {
              print "$role=$href->{$role} ";
          }
          print "}\n";
      }

      # print the whole thing with indices
      for $i ( 0 .. $#AoH ) {
          print "$i is { ";
          for $role ( keys %{ $AoH[$i] } ) {
              print "$role=$AoH[$i]{$role} ";
          }
          print "}\n";
      }

      # print the whole thing one at a time
      for $i ( 0 .. $#AoH ) {
          for $role ( keys %{ $AoH[$i] } ) {
              print "elt $i $role is $AoH[$i]{$role}\n";
          }
      }

HASHES OF HASHES


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     Declaration of a HASH OF HASHES

      %HoH = (
             flintstones => {
                     lead      => "fred",
                     pal       => "barney",
             },
             jetsons     => {
                     lead      => "george",
                     wife      => "jane",
                     "his boy" => "elroy",
             },
             simpsons    => {
                     lead      => "homer",
                     wife      => "marge",
                     kid       => "bart",
             },
      );

     Generation of a HASH OF HASHES

      # reading from file
      # flintstones: lead=fred pal=barney wife=wilma pet=dino
      while ( <> ) {
          next unless s/^(.*?):\s*//;
          $who = $1;
          for $field ( split ) {
              ($key, $value) = split /=/, $field;
              $HoH{$who}{$key} = $value;
          }

      # reading from file; more temps
      while ( <> ) {
          next unless s/^(.*?):\s*//;
          $who = $1;
          $rec = {};
          $HoH{$who} = $rec;
          for $field ( split ) {
              ($key, $value) = split /=/, $field;
              $rec->{$key} = $value;
          }
      }

      # calling a function  that returns a key,value hash
      for $group ( "simpsons", "jetsons", "flintstones" ) {
          $HoH{$group} = { get_family($group) };
      }

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      # likewise, but using temps
      for $group ( "simpsons", "jetsons", "flintstones" ) {
          %members = get_family($group);
          $HoH{$group} = { %members };
      }

      # append new members to an existing family
      %new_folks = (
          wife => "wilma",
          pet  => "dino",
      );

      for $what (keys %new_folks) {
          $HoH{flintstones}{$what} = $new_folks{$what};
      }

     Access and Printing of a HASH OF HASHES

      # one element
      $HoH{flintstones}{wife} = "wilma";

      # another element
      $HoH{simpsons}{lead} =~ s/(\w)/\u$1/;

      # print the whole thing
      foreach $family ( keys %HoH ) {
          print "$family: { ";
          for $role ( keys %{ $HoH{$family} } ) {
              print "$role=$HoH{$family}{$role} ";
          }
          print "}\n";
      }

      # print the whole thing  somewhat sorted
      foreach $family ( sort keys %HoH ) {
          print "$family: { ";
          for $role ( sort keys %{ $HoH{$family} } ) {
              print "$role=$HoH{$family}{$role} ";
          }
          print "}\n";
      }

      # print the whole thing sorted by number of members
      foreach $family ( sort { keys %{$HoH{$b}} <=> keys %{$HoH{$a}} } keys %HoH ) {
          print "$family: { ";
          for $role ( sort keys %{ $HoH{$family} } ) {
              print "$role=$HoH{$family}{$role} ";
          }
          print "}\n";
      }

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      # establish a sort order (rank) for each role
      $i = 0;
      for ( qw(lead wife son daughter pal pet) ) { $rank{$_} = ++$i }

      # now print the whole thing sorted by number of members
      foreach $family ( sort { keys %{ $HoH{$b} } <=> keys %{ $HoH{$a} } } keys %HoH ) {
          print "$family: { ";
          # and print these according to rank order
          for $role ( sort { $rank{$a} <=> $rank{$b} }  keys %{ $HoH{$family} } ) {
              print "$role=$HoH{$family}{$role} ";
          }
          print "}\n";
      }

MORE ELABORATE RECORDS

     Declaration of MORE ELABORATE RECORDS

     Here's a sample showing how to create and use a record whose
     fields are of many different sorts:

          $rec = {
              TEXT      => $string,
              SEQUENCE  => [ @old_values ],
              LOOKUP    => { %some_table },
              THATCODE  => \&some_function,
              THISCODE  => sub { $_[0] ** $_[1] },
              HANDLE    => \*STDOUT,
          };

          print $rec->{TEXT};

          print $rec->{SEQUENCE}[0];
          $last = pop @ { $rec->{SEQUENCE} };

          print $rec->{LOOKUP}{"key"};
          ($first_k, $first_v) = each %{ $rec->{LOOKUP} };

          $answer = $rec->{THATCODE}->($arg);
          $answer = $rec->{THISCODE}->($arg1, $arg2);

          # careful of extra block braces on fh ref
          print { $rec->{HANDLE} } "a string\n";

          use FileHandle;
          $rec->{HANDLE}->autoflush(1);
          $rec->{HANDLE}->print(" a string\n");

     Declaration of a HASH OF COMPLEX RECORDS

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          %TV = (
             flintstones => {
                 series   => "flintstones",
                 nights   => [ qw(monday thursday friday) ],
                 members  => [
                     { name => "fred",    role => "lead", age  => 36, },
                     { name => "wilma",   role => "wife", age  => 31, },
                     { name => "pebbles", role => "kid",  age  =>  4, },
                 ],
             },

             jetsons     => {
                 series   => "jetsons",
                 nights   => [ qw(wednesday saturday) ],
                 members  => [
                     { name => "george",  role => "lead", age  => 41, },
                     { name => "jane",    role => "wife", age  => 39, },
                     { name => "elroy",   role => "kid",  age  =>  9, },
                 ],
              },

             simpsons    => {
                 series   => "simpsons",
                 nights   => [ qw(monday) ],
                 members  => [
                     { name => "homer", role => "lead", age  => 34, },
                     { name => "marge", role => "wife", age => 37, },
                     { name => "bart",  role => "kid",  age  =>  11, },
                 ],
              },
           );

     Generation of a HASH OF COMPLEX RECORDS

          # reading from file
          # this is most easily done by having the file itself be
          # in the raw data format as shown above.  perl is happy
          # to parse complex data structures if declared as data, so
          # sometimes it's easiest to do that

          # here's a piece by piece build up
          $rec = {};
          $rec->{series} = "flintstones";
          $rec->{nights} = [ find_days() ];

          @members = ();
          # assume this file in field=value syntax
          while (<>) {
              %fields = split /[\s=]+/;
              push @members, { %fields };
          }
          $rec->{members} = [ @members ];

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          # now remember the whole thing
          $TV{ $rec->{series} } = $rec;

          ###########################################################
          # now, you might want to make interesting extra fields that
          # include pointers back into the same data structure so if
          # change one piece, it changes everywhere, like for example
          # if you wanted a {kids} field that was a reference
          # to an array of the kids' records without having duplicate
          # records and thus update problems.
          ###########################################################
          foreach $family (keys %TV) {
              $rec = $TV{$family}; # temp pointer
              @kids = ();
              for $person ( @{ $rec->{members} } ) {
                  if ($person->{role} =~ /kid|son|daughter/) {
                      push @kids, $person;
                  }
              }
              # REMEMBER: $rec and $TV{$family} point to same data!!
              $rec->{kids} = [ @kids ];
          }

          # you copied the array, but the array itself contains pointers
          # to uncopied objects. this means that if you make bart get
          # older via

          $TV{simpsons}{kids}[0]{age}++;

          # then this would also change in
          print $TV{simpsons}{members}[2]{age};

          # because $TV{simpsons}{kids}[0] and $TV{simpsons}{members}[2]
          # both point to the same underlying anonymous hash table

          # print the whole thing
          foreach $family ( keys %TV ) {
              print "the $family";
              print " is on during @{ $TV{$family}{nights} }\n";
              print "its members are:\n";
              for $who ( @{ $TV{$family}{members} } ) {
                  print " $who->{name} ($who->{role}), age $who->{age}\n";
              }
              print "it turns out that $TV{$family}{lead} has ";
              print scalar ( @{ $TV{$family}{kids} } ), " kids named ";
              print join (", ", map { $_->{name} } @{ $TV{$family}{kids} } );
              print "\n";
          }

Database Ties

     You cannot easily tie a multilevel data structure (such as a
     hash of hashes) to a dbm file.  The first problem is that

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     all but GDBM and Berkeley DB have size limitations, but
     beyond that, you also have problems with how references are
     to be represented on disk.  One experimental module that
     does partially attempt to address this need is the MLDBM
     module.  Check your nearest CPAN site as described in perl-
     modlib for source code to MLDBM.

SEE ALSO

     perlref(1), perllol(1), perldata(1), perlobj(1)

AUTHOR

     Tom Christiansen <tchrist@perl.com>

     Last update: Wed Oct 23 04:57:50 MET DST 1996

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