• NAME
• DESCRIPTION
• REFERENCES
• COMMON MISTAKES
• CAVEAT ON PRECEDENCE
• WHY YOU SHOULD ALWAYS use strict
• DEBUGGING
• CODE EXAMPLES
• LISTS OF LISTS
  • Declaration of a LIST OF LISTS
  • Generation of a LIST OF LISTS
  • Access and Printing of a LIST OF LISTS
• HASHES OF LISTS
  • Declaration of a HASH OF LISTS
  • Generation of a HASH OF LISTS
  • Access and Printing of a HASH OF LISTS
• LISTS OF HASHES
  • Declaration of a LIST OF HASHES
  • Generation of a LIST OF HASHES
  • Access and Printing of a LIST OF HASHES
• HASHES OF HASHES
  • Declaration of a HASH OF HASHES
  • Generation of a HASH OF HASHES
  • Access and Printing of a HASH OF HASHES
• MORE ELABORATE RECORDS
  • Declaration of MORE ELABORATE RECORDS
  • Declaration of a HASH OF COMPLEX RECORDS
  • Generation of a HASH OF COMPLEX RECORDS
• Database Ties
• SEE ALSO
• AUTHOR

NAME

DESCRIPTION

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 a array with three dimensions!

    for $x (1 .. 10) {
        for $y (1 .. 10) {
            for $z (1 .. 10) {
                $LoL[$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 @LoL? How do you sort it? How can you pass it to a function or get one of these back from a function? Is is 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 purloin a drop-in example from here.

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

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 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 the perlmodlib manpage 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

Source: Perl manual pages Copyright: Larry Wall, et al.