This and other RFCs are available on the web at http://dev.perl.org/rfc/ =head1 TITLE my() syntax extensions and attribute declarations =head1 VERSION Maintainer: Nathan Wiger <[EMAIL PROTECTED]> Date: 24 Sep 2000 Last Modified: 30 Sep 2000 Mailing List: [EMAIL PROTECTED] Number: 279 Version: 2 Status: Frozen =head1 ABSTRACT This RFC fleshes out variable declarations with C<my>, and also proposes a way to assign attributes without the need for a C<my> anywhere. Much of this stuff has been hinted at, so this is just a formalization. Please note this entire document is B<optional>, intended for those that need this type of control. Perl is not a B&D language (by default, at least :). =head1 DESCRIPTION Camel-3 shows some interesting hints of what's been proposed for C<my> declarations: my type $var :attr1 :attr2 = $value; And we all know that you can use C<my> to declare a group of variables: my($x, $y, $z); Here's the issues: 1. How do the two jive together? 2. Should it be possible to assign attributes to individual elements of hashes/arrays? (yes) =head2 Cohesive C<my> syntax This RFC proposes that you be able to group multiple variables of the same type within parens: my int ($x, $y, $z); my int ($x :64bit, $y :32bit, $z); It seems most logical that: 1. The type will be the same across variables; this is common usage in other languages because it makes sense. 2. The attributes will be different for different variables. As such, multiple attributes can be assigned and grouped flexibly: my int ($x, $y, $z) :64bit; # all are 64-bit my int ($x, $y, $z :unsigned) :64bit; # plus $z is unsigned Note that multiple types cannot be specified on the same line. To declare variables of multiple types, you must use separate statements: my int ($x, $y, $z) :64bit; my string ($firstname, $lastname :long); This is consistent with other languages and also makes parsing realistic. =head2 Assigning attributes to individual elements of hashes/arrays This is potentially very useful. ":laccess", ":raccess", ":public", ":private", and others spring to mind as potential candidates for this. This RFC proposes that in addition to attributes being assigned to a whole entity on declaration: my int @a :64bit; # makes each element a 64-bit int my string %h :long; # each key/val is long string They can also be declared on individual elements, without the need for C<my> or C<our>: $a[0] :32bit = get_val; # 32-bit $r->{name} :private = "Nate"; # privatize single value $s->{VAL} :laccess('data') = ""; # lvalue autoaccessor Assigning attributes to individual elements has the advantage over keywords of allowing them to be grouped: $self->{name} :public :roaccess('getname') = "Nathan Wiger"; However, a problem arises in how to assign types to singular elements, since this requires a C<my>: my int $a[0] :64bit; # just makes that single element # a lexically-scoped 64-bit int? my string $h{name} = ""; # cast $h{name} to string, rescope %h? Currently, lexical scope has no meaning for individual elements of hashes and arrays. However, assigning attributes and even types to individual elements seems useful. There's two ways around this that I see: 1. On my'ing of an individual hash/array element, the entire hash/array is rescoped to the nearest block. 2. Only the individual element is rescoped, similar to what happens when you do this: my $x = 5; { my $x = 10; } Either of these solutions is acceptable, and they both have their pluses and minuses. The second one seems more consistent, but is potentially extremely difficult to implement. =head1 IMPLEMENTATION Hold on. =head1 MIGRATION None. This introduces a more flexible syntax but does not break old ones. =head1 REFERENCES RFC 337: Common attribute system to allow user-defined, extensible attributes RFC 319: Transparently integrate C<tie> Camel for the C<my> syntax. C<attributes> man page for details on attributes.
