I haven't found a heck of a lot of documentation about pseudo-hashes outside of Damian Conway's "Object Oriented Perl" book. For those unfamiliar with a pseudo-hash, it's an new feature as of Perl 5.005. According to Programming Perl, third edition, a pseudo-hash is any array reference whose first field is a hash reference. This hash reference should be a mapping of hash keys and array elements for the subsequent elements in the array reference. Confused yet? Here's some code: 
use warnings;
use strict;

my $ph = [ { alpha => 1, beta => 2, gamma => 3, delta => 4, epsilon =>
+ 5 }, #hashref
             "val a",    "val b",   "val c",    "val d",    "val e" ];
+ # maps to these values

# Print some of the elements
print $ph->[1], "\n";
print $ph->{ alpha }, "\n";
print $ph->{ epsilon }, "\n";

# Let's add an element
# Note the amount of work involved (though this can be done on two lin
+es)
# We can't autovivify an entry!!
$ph->[ $ph->[ 0 ]->{ omega } = @{ $ph } ] = "The real last val";

print $ph->{ omega };

[download]
Now we can use an array as either a hash or array, supposedly getting the best of both worlds. Of course, this really needs both a hash lookup and an array lookup and thus has extra overhead unless we use the fields module. And, of course, deleting keys is problematic, and the syntax is confusing, and...

This leads me to wonder... what problem do pseudo-hashes solve? I know there's the annoyance with a regular hash autovivifying hash entries. Pseudo-hashes don't allow for autovivification of entries and can prevent subtle logic problems. But is this the only benefit? And is it potent enough to justify the extra work involved with creating one?

Cheers,
Ovid

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In reply to Are pseudo-hashes worth the effort? by Ovid

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