Hey, this RFC stuff is fun!
=head1 TITLE
variable usage warnings
=head1 VERSION
Maintainer: Steve Fink <[EMAIL PROTECTED]> for now
Date: 2 Aug 2000
Version: 0 (unreleased)
Mailing List: [EMAIL PROTECTED]
Number: (unassigned)
=head1 ABSTRACT
"VARIABLE used only once: possible typo" should be replaced with
warnings on uses of uninitialized variables (including lexicals).
=head1 DESCRIPTION
Perl6 should distinguish between uses and assignments to variables,
and warn only when a variable is used without being assigned. In
perl5 the complete program
$x = 3
complains, but
$x = 3; $x = 3
does not, nor does
my $x = 3
nor
use vars qw($x $y); $x = $z; $y = $z;
It would be more useful to have a complaint for both lexical and
package variables, and only when a variable is used without ever being
assigned to (or having its reference taken).
The warning message "use of uninitialized value" should also
disappear, to be replaced with "use of undefined value", and the
warning for the purpose described in this RFC should be "use of
uninitialized variable C<$x>".
Note that if you currently depend on lexical variables having
undefined values, you would need to change C<my $x> to C<my $x =
undef>. This is a Good Thing.
=head1 IMPLEMENTATION
I have no idea how difficult this would be to implement. You just need
to distinguish between lvalue and rvalue uses of a variable, I guess?
But hey, this is a language RFC, not an internals RFC. :-) There's
also the question of whether to properly track uses and definitions so
that C<$::z = $x; $x = 3> is a warning, as well as C<$x = 3 if f();
print $x>. Though the latter would require renaming the warning to
"possible use of uninitialized variable C<$x>".
