On Thu, 14 Nov 2002 11:49:56 +1100, Ken Williams wrote:
>
>On Thursday, November 14, 2002, at 07:17 AM, Brian Ingerson wrote:
>
>>On 13/11/02 16:08 +0100, [EMAIL PROTECTED] wrote:
>>>
>>>A problem we had with dynamic loading of Inline modules has been
>>>tracked down to the use of $_ in Inline::denter.
>>>With the attached patch it works OK
>>
>>Wow. That's crazy. How could $_ affect anything? Would you mind
>>sending a brief expanation? I'll apply the patch.
>
>$_ is a global variable just like any other. If you clobber it, you
>may clobber someone else's data.
>
>The reason $_ is usually safe is that you don't generally assign
>things to it, you let perl do the assigning implicitly (by using a
>foreach(), map(), grep(), etc.) and in this case it localizes the
>variable before assignment.
>
>But if you assign explicitly and you don't localize, clobber city.
The code snippet
$_ =
is usually a BAD THING. Don't do it.
>The following script demonstrates:
>
>#!/usr/bin/perl
>
>top();
>
>sub top { local $_ = 5;
>inner();
>print "\$_ is $_\n";
>}
>
>sub inner { $_ = 7;
>}
>
>__END__
>
>
>>*************** *** 188,193 **** --- 189,195 ----
>>$o->{done}++, $o->{level} = -1, return unless @{$o->{lines}};
>>my ($width, $tabwidth) = @{$o}{qw(width tabwidth)};
>>while (1) { + local ($_);
>>$_ = $o->{lines}[0];
>
>Incidentally, I'd just write these as
>
>local $_ = $o->{lines}[0];
As explained, you usually use $_ as assigned by Perl in for, map
,grep. From these snippets, it seems like $_ is being assigned and
used because:
1) being too lazy (bad lazy) to use a 'my' 2) misguidedly think that
not using 'my' saves a significant number of cycles 3) being too
cute. Instead of
local ($_);
$_ = $o->{lines}[0];
$o->next_line, next if /^(\s*$|\#)/; # skip comments and blank lines
use a my $x and write
my $x = $o->{lines}[0];
$o->next_line, next if $x=~ m/^(\s*$|\#)/; # skip comments and blank lines
Or, even more concisely,
$o->next_line, next if $o->{lines}[0];=~m/^(\s*$|\#)/; # skip comments and blank
lines
And in the case of this fragment:
sub indent_data {
my $o = shift;
local ($_);
$_ = shift;
return $o->indent_undef($_)
why not:
sub indent_data {
my $o = shift;
return $o->indent_undef(shift);
or even:
sub indent_data {
return shift()->indent_undef(shift);
Yes, that last one really works! I tested it. talk about DWIM.
--
Matthew O. Persico
