Beginning with release 5.005 of Perl you can use an array reference in some contexts that would normally require a hash reference. This allows you to access array elements using symbolic names, as if they were fields in a structure.

For this to work, the array must contain extra information. The first element of the array has to be a hash reference that maps field names to array indices. Here is an example:

   $struct = [{foo => 1, bar => 2}, "FOO", "BAR"];


   $struct->{foo};  # same as $struct->[1], i.e. "FOO"
   $struct->{bar};  # same as $struct->[2], i.e. "BAR"

   keys %$struct;   # will return ("foo", "bar") in some order
   values %$struct; # will return ("FOO", "BAR") in same some order

   while (my($k,$v) = each %$struct) {
       print "$k => $v\n";
   }
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- Zoogie

That's pretty cool. I wonder what it's good for.

This is just a guess (perhaps somebody who's more experienced with Perl compiler optimizations can help out here). Since accessing array elements tends to be faster than accessing hash elements, if the Perl compiler resolves the pseudo-hash keys to the array indexes at compile-time, it makes building structures with named elements more efficient at run-time than simply using hashes.

The perlref page notes that the compiler does something to this effect for using named fields in objects. I'm not at all familiar with objects in Perl, so I can't really elaborate on that.

- Zoogie