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Re: Why are subs matching /^[\W_]$/ global?
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From:
Ævar Arnfjörð Bjarmason
Date:
June 2, 2010 07:45
Subject:
Re: Why are subs matching /^[\W_]$/ global?
Message ID:
AANLkTilFCpdepoPcleqlWAHpMQtiO2eYzYp8VNXkiDy1@mail.gmail.com
On Wed, Jun 2, 2010 at 14:18, Abigail <abigail@abigail.be> wrote:
> On Wed, Jun 02, 2010 at 02:03:26PM +0000, Ævar Arnfjörð Bjarmason wrote:
>> On Wed, Jun 2, 2010 at 13:13, Abigail <abigail@abigail.be> wrote:
>> > On Wed, Jun 02, 2010 at 12:46:44PM +0000, Ęvar Arnfjörš Bjarmason wrote:
>> >> Single-character non-alpha (plus _) subroutines are global
>> >>
>> >> $ perl -le '** = sub {warn "Hi"}; package Foo; &*'
>> >> Hi at -e line 1.
>> >>
>> >> $ perl -le '*a = sub {warn "Hi"}; package Foo; &a'
>> >> Undefined subroutine &Foo::a called at -e line 1.
>> >>
>> >> and:
>> >>
>> >> $ perl -le '*_ = sub {warn "Hi"}; package Foo; &_'
>> >> Hi at -e line 1.
>> >>
>> >> $ perl -le '*__ = sub {warn "Hi"}; package Foo; &__'
>> >> Undefined subroutine &Foo::__ called at -e line 1
>> >>
>> >> This came up when I was looking at _() in Perl as a potential Gettext
>> >> wrapper (I know about the _ filehandle).
>> >>
>> >> _ I think I can understand (presumably the _ glob is global). But why
>> >> does this apply generally to all /^[\W_]$/ subs? Is it explicitly
>> >> documented somewhere? Perhaps it's something we'd want to deprecate?
>> >>
>> >
>> >
>> > Documented. From perlvar:
>> >
>> > Perl identifiers that begin with digits, control characters, or
>> > punctuation characters are exempt from the effects of the "package"
>> > declaration and are always forced to be in package "main"; they are
>> > also exempt from "strict 'vars'" errors. A few other names are also
>> > exempt in these ways:
>> >
>> > ENV STDIN
>> > INC STDOUT
>> > ARGV STDERR
>> > ARGVOUT _
>> > SIG
>> >
>> > In particular, the new special "${^_XYZ}" variables are always taken to
>> > be in package "main", regardless of any "package" declarations
>> > presently in scope.
>> >
>> >
>> > Note also that perlvar claims all such names are reserved for special uses
>> > by Perl. From the same manual page:
>>
>> Thanks. I was looking in perlsub and friends.
>>
>> > Perl variable names may also be a sequence of digits or a single
>> > punctuation or control character. These names are all reserved for
>> > special uses by Perl; for example, the all-digits names are used to
>> > hold data captured by backreferences after a regular expression match.
>> > Perl has a special syntax for the single-control-character names: It
>> > understands "^X" (caret "X") to mean the control-"X" character. For
>> > example, the notation $^W (dollar-sign caret "W") is the scalar
>> > variable whose name is the single character control-"W". This is
>> > better than typing a literal control-"W" into your program.
>> >
>> >
>> > Basically, it comes down to, "if it global, you can't have it anyway".
>>
>> Right, but if it's reserved by perl, perhaps we should warn and
>> eventually prohibit uses of these constructs. As-is you can define and
>> use a sub called *, even though it's reserved.
>
>
> Why? It has worked for over a dozen years or so. So what if someone
> defines a sub &,. I don't see p5p making &, a core function anytime soon.
>
> It might have been something to prohibit when 5.000 was developed, but
> I don't see any benefits to warn, and later prohibit this now.
To reduce the mismatch between what the POD claims, and what the
implementation actually does. That there isn't even a warning when you
use something that's "reserved for special uses by Perl" seems like an
implementation omission.
It'd also be friendly if this:
package Meh;
use warnings 'danger_will_robinson';
sub x {}
sub _ {}
Noted to the naïve user that Perl's magically using odd scope
semantics for "_" that don't apply to "x". That's the reason I ran
into this.
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