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Postings from June 2010
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.
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