AW: _ handle and sub _
-Ursprüngliche Nachricht-
Von: Rafael Garcia-Suarez [mailto:[EMAIL PROTECTED]
Gesendet: Montag, 5. September 2005 16:24
An: Dintelmann, Peter
Cc: perl5-porters@perl.org
Betreff: Re: _ handle and sub _
On 9/5/05, Dintelmann, Peter [EMAIL PROTECTED] wrote:
When a subroutine _ is defined it may mask the _ handle used
by file test operators.
#!/opt/perl32/bin/perl
use strict;
use warnings;
sub _ { /etc/hosts }
open my $f, /dev/null or warn $!;
stat $f or warn $!;
print size: , -s _, \n;
In the last line sub _ is invoked and the script prints the size
of /etc/hosts instead of 0.
However -X *_ seems to get this right. Should we mention this in
perlfunc?
I don't think so, since this behaviour is the same with any other
identifier.
Certainly, but _ is in main which may cause problems with modules.
Here is a simple example using File::Find which resembles the problem I
was originally debubbing.
#!/opt/perl32/bin/perl -l
use strict;
BEGIN { sub _ {1} }
use File::Find; # _ handle used in File::Find
my $cnt = 0;
find sub {$cnt++}, /etc;
print $cnt; # 1 instead of 815 on my system
Replacing the _ handle with *_ in the module saved my day (do you think
we should patch File::Find?) which reminds me about the usage of
local $_ in modules.
Though the choice of _ as a sub name may be problematic as pointed out
by MJD there is existing code which uses it already.
_ handle and sub _
When a subroutine _ is defined it may mask the _ handle used
by file test operators.
#!/opt/perl32/bin/perl
use strict;
use warnings;
sub _ { /etc/hosts }
open my $f, /dev/null or warn $!;
stat $f or warn $!;
print size: , -s _, \n;
In the last line sub _ is invoked and the script prints the size
of /etc/hosts instead of 0.
However -X *_ seems to get this right. Should we mention this in
perlfunc?
--- /opt/perl32/lib/5.8.7/pod/perlfunc.pod Wed Jun 1 16:20:40 2005
+++ /var/tmp/perlfunc.pod Mon Sep 5 17:05:06 2005
@@ -366,6 +366,10 @@
print Text\n if -T _;
print Binary\n if -B _;
+If a function named C_ is defined, the file tests will operate on its
+return value instead of the saved stat structure. Replace C-X _ with
+C-X *_ to circumvent this behaviour.
+
=item abs VALUE
=item abs
Re: _ handle and sub _
On 9/5/05, Dintelmann, Peter [EMAIL PROTECTED] wrote:
When a subroutine _ is defined it may mask the _ handle used
by file test operators.
#!/opt/perl32/bin/perl
use strict;
use warnings;
sub _ { /etc/hosts }
open my $f, /dev/null or warn $!;
stat $f or warn $!;
print size: , -s _, \n;
In the last line sub _ is invoked and the script prints the size
of /etc/hosts instead of 0.
However -X *_ seems to get this right. Should we mention this in
perlfunc?
I don't think so, since this behaviour is the same with any other identifier.
Re: _ handle and sub _
When a subroutine _ is defined it may mask the _ handle used by file test operators. There are a number of problems with using '_' as a subroutine name; this is one of the simplest and most predictable. '__' is apparently a much safer choice. See http://hop.perl.plover.com/errata/byid.cgi/131 for a discussion of some of the additional problems with '_'. +If a function named C_ is defined, the file tests will operate on its +return value instead of the saved stat structure. Replace C-X _ with +C-X *_ to circumvent this behaviour. This strikes me as one of those additions to the manual that is well-meaning but not worth the space it requires. The problem it is designed to addres is uncommon, and the fraction of people who encounter that problem who actually look in the right part of the manual, find the new remark, and recognize its significance will be vanishingly small.
Re: _ handle and sub _
Also: http://hop.perl.plover.com/~alias/list.cgi?2:mss:264
