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
Mailing List: [EMAIL PROTECTED]
Number: 279
Version: 1
Status: Developing
=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.
=head1 DESCRIPTION
Camel-3 shows some interesting hints of what's been proposed for C<my>
declarations:
my type $var :attribute = $value;
And we all know that you can use C<my> to declare a group of variables:
my($x, $y, $z);
Here's the issues:
1. How do the two jive together?
2. Should it be possible to assign attributes to individiual elements
of hashes/arrays? (yes)
=head2 Cohesive C<my> syntax
This RFC proposes that you be able to group multiple variables of the
same type within parens:
my int ($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 assignable to a
whole entity:
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>:
$a[0] :32bit = get_val; # 32-bit
$r->{name} :private = "Nate"; # privatize single value
$s->{VAL} :laccess('data') = ""; # lvalue autoaccessor
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
Camel for the C<my> syntax.
