On Fri, 25 Aug 2000, Rick Myers wrote:
> On Aug 24, 2000 at 23:15:15 -0500, Ken Williams twiddled the keys to say:
> > [EMAIL PROTECTED] (Rick Myers) wrote:
> > >On Aug 24, 2000 at 01:15:57 -0500, Ken Williams twiddled the keys to say:
> > >> The following patch eliminates a warning during 'make test' about 'Value
> > >> of <HANDLE> construct can be "0";'. No biggie, but it should be fixed.
> > >>
> > >> ________________________________________________________________
> > >> --- t/modules/request.t 2000/05/12 03:43:24 1.8
> > >> +++ t/modules/request.t 2000/08/24 06:07:40
> > >> @@ -125,7 +125,7 @@
> > >> my $lines = 0;
> > >> local *FH;
> > >> open FH, $file or die "open $file $!";
> > >> - ++$lines while (my $dummy = <FH>);
> > >> + ++$lines while <FH>;
> > >> close FH;
> > >> my(@headers);
> > >> if ($Is_dougm) {
> > >> ________________________________________________________________
> > >
> > >This reverses a previous patch that fixes a fatal 'Modification of a
> > >read-only value attempted at modules/request.t line 128', which returns
> > >with this patch.
> > >
> > >See if this one finds us a happy median...
> > >
> > >--- t/modules/request.t~ Thu Aug 24 18:24:39 2000
> > >+++ t/modules/request.t Thu Aug 24 18:41:22 2000
> > >@@ -125,7 +125,7 @@
> > > my $lines = 0;
> > > local *FH;
> > > open FH, $file or die "open $file $!";
> > >- ++$lines while (my $dummy = <FH>);
> > >+ ++$lines while defined <FH>;
> > > close FH;
> > > my(@headers);
> > > if ($Is_dougm) {
> >
> >
> > THAT's weird - what in the world is the read-only value that's being
> > modified?
>
> It's $_.
>
> Here's the relevant code from request.t to illustrate...
>
> for ( qw(perlfunc.pod perlpod.pod perlxs.pod), @binary) {
> upload_test($_);
> }
>
> sub upload_test {
> ++$lines while <FH>;
> }
The real fix should be either:
for my $file ( qw(perlfunc.pod perlpod.pod perlxs.pod), @binary) {
upload_test($file);
}
sub upload_test {
++$lines while <FH>;
}
or
for ( qw(perlfunc.pod perlpod.pod perlxs.pod), @binary) {
upload_test($_);
}
sub upload_test {
local $_;
++$lines while <FH>;
}
The really one and the only correct one is of course:
for my $file ( qw(perlfunc.pod perlpod.pod perlxs.pod), @binary) {
upload_test($file);
}
sub upload_test {
local $_;
++$lines while <FH>;
}
You are trying to workaround the problem. It's always becomes very subtle
to find bug when you do:
for (1..5) { function($_) }
Because you never know whether the function itself is using $_ and
modifying it. In this situation you are lucky that the list you pass to
the for is readonly -- perl reports a problem. A much worth thing happen
when the variable that you pass to for() is a real array:
for (@array) { function($_) }
$_ is aliased to the real variables in @array -- it's not a copy!!! So if
function() alters $_, your array gets changed!!! This is a side effect
which can byte you very badly.
Therefore, if you are a good perl programmer and want your code to be
clean, when you write subroutines which work with $_, always start them
with:
local $_;
If you write for() and similar loops that alias $_ to the real variables
in the list, *always* do:
for my $val (@array) { foo($val) }
use $_ only if the loop doesn't call any function unless you are sure that
the function declares 'local $_';. The following is a perfect snippet of
code:
my $count = 0;
for (@values){
$count += $_;
}
>
> The hint is that `while <FH>' will try to set $_ to the value of each
> line read.
>
> Rick Myers [EMAIL PROTECTED]
> ----------------------------------------------------
> The Feynman Problem 1) Write down the problem.
> Solving Algorithm 2) Think real hard.
> 3) Write down the answer.
>
_____________________________________________________________________
Stas Bekman JAm_pH -- Just Another mod_perl Hacker
http://stason.org/ mod_perl Guide http://perl.apache.org/guide
mailto:[EMAIL PROTECTED] http://apachetoday.com http://jazzvalley.com
http://singlesheaven.com http://perlmonth.com perl.org apache.org
