(aka Multidimensional Arrays/Hashes)
Reply-To: [EMAIL PROTECTED]
This and other RFCs are available on the web at
http://dev.perl.org/rfc/
=head1 TITLE
A Natural Syntax Extension For Chained References
(aka Multidimensional Arrays/Hashes)
=head1 VERSION
Maintainer: Jarkko Hietaniemi <[EMAIL PROTECTED]>
Date: 29 Aug 2000
Mailing List: [EMAIL PROTECTED]
Version: 1
Number: 177
Status: Developing
=head1 ABSTRACT
In this RFC an extension to existing Perl syntax is proposed. The
syntax doesn't conflict with anything existing (in fact it corrects a
bug of sorts), it is natural (naturalness being naturally in the eye
of the proposer), and it gives concise way to express a complex data
structure access.
=head1 DESCRIPTION
Snatch two syntax constructs away from the jaws of illegal syntax and
an unfortunate syntax, and make them useful weapons of the Perl
arsenal. The constructs are:
$ref->[[LIST]]
$ref->{{LIST}}
The proposed respective meanings:
$ref->[$elem[0]]->[$elem[1]}->[...]->[$elem[-1]]
$ref->{$elem[0]}->{$elem[1]}->{...}->{$elem[-1]}
That is, the lists are being expanded as the indices for a chain of
references, the arrays could be called index lists. Having the
indices in one place saves a lot of characters. Compare
$r->{{qw(a b c d e f g h)}}
versus
$r->{a}->{b}->{c}->{d}->{e}->{f}->{g}->{h}
An example using an array may be even more enticing
$r->[[@a]]
versus
$r->[$a[0]]->[$a[1]]->...
or even
$r->[$a]->[$b]->...
(assuming @a = ($a, $b, ...))
As mentioned earlier, these syntaxes do not do anything useful at the moment.
The first one, ->[[]], is an intermittent cause of segmentation
violations, core dumps, and bug reports because it already does have a
meaning but a rather twisted and faulty one: "access the array at the
offset of stringifying this anonymous list". This offset is usually a
rather large one, resulting in unruly memory access attempts. Reusing
the syntax for something useful cannot be an evil thing.
The second one, ->{{}}, is currently a syntax error, and cannot
therefore broke existin code.
The degenerate case of the list being empty can be defined to be
equivalent to $ref.
=head1 IMPLEMENTATION
Since the exact meaning of the construct depends on the contents of
the index list, the chasing the indices (autovivifying data structures
as needed) cannot be determined in compile time and needs to be
a run-time operation.
=head1 REFERENCES
perlref
perldsc
perllol
