Front page | perl.perl5.porters |
Postings from August 2008
On Wed Aug 06 00:47:57 2008, drahflow@gmx.de wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Testcase:
>
> #/usr/bin/perl
>
> use Carp;
> use strict;
> use warnings;
>
> $::{'a'} = sub { print "a\n"; };
> $::{'b'} = sub { print "b\n"; };
> # *::a = sub { print "a\n"; };
> # *::b = sub { print "b\n"; };
>
> a();
>
> eval "a()"; confess $@ if $@;
> eval "b()"; confess $@ if $@;
>
>
> Output:
>
> a
> a
> Undefined subroutine &main::b called at (eval 2) line 1.
> at test.pl line 15
>
> Plain English Version:
>
> Something odd is happening if a sub reference is assigned to a
> symbol table entry. In particular, the behaviour is different
> from the behaviour encountered if said assignment goes through
> the typeglob. This can easily be checked, if the commented lines
> are put in, and the other assignments commented out.
>
> Also the oddness can be modified by calling the sub directly
> somewhere else, presumably because this will create or change
> the respective symbol table entry.
>
> This difference might seem totally insignificant. If the names
> "a" and "b" are supplied dynamically however, the non-working
> version is IMHO superior (apart from its non-working), because
> there will be no need for an eval, and neither one for symbolic
> de-referencing.
>
> The documentation in "perlmod" seems to imply that the typeglob
> and the symbol table entry are one and the same, so if this is
> considered correct behaviour, maybe the docs should be mended.
>
> Best Regards,
> Jens-W. Schicke
>
Easier examples:
$ perl -le '$main::{foo} = \"a"; eval "print \$foo;";'
(no output - a was 'expected')
$ perl -wle '$main::{foo} = \"a"; eval "print \$foo;";$_=$foo;'
Name "main::foo" used only once: possible typo at -e line 1.
a
$ perl -wle '*foo = \"a"; eval "print \$foo;";'
Name "main::foo" used only once: possible typo at -e line 1.
a
Another example:
$ cat rt-57646.pl
print $main::foo;
$ perl -wle '$main::{foo} = \"a"; require "rt-57646.pl";'
Use of uninitialized value in print at rt-57646.pl line 1.
('a' was 'exepected' instead of undef)
$ perl -wle '$main::{foo} = \"a"; require "rt-57646.pl";$_=$foo;'
Name "main::foo" used only once: possible typo at -e line 1.
a
This behaviour goes back to at least 5.00504.
I vote to remove the line:
local $main::{foo} = $main::{bar};
from the documentation in perlmod.
It seems to me that explaining that it needs a reference to *foo which
is known at compile time is going to be more confusing then simple
removing it. (Unless someone wants to take a try at fixing this
behavoiur?)
Patch that removes the text is attached.
Kind regards,
Bram
Thread Next