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Jul 3, 2012, 9:44 PM
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[perl #86136] strange inconsistency in detecting Can't use "my $b" in sort comparison
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On Tue Jun 05 09:27:47 2012, sprout wrote:
> On Mon Mar 14 09:22:34 2011, nicholas wrote:
> > This one makes no sense to me:
> >
> > $ cat eval.pl
> > #!./perl
> >
> > use strict;
> > use warnings;
> >
> > my $b = 'wrong';
> >
> > my @a = sort
> > { print; $a <=> $b }
> > 2, 1;
> >
> > BEGIN {
> > print "Got here\n";
> > }
> >
> > my @b = sort
> > { func(); $a <=> $b }
> > 2, 1;
> > ./perl -Ilib eval.pl
> > Got here
> > Can't use "my $b" in sort comparison at eval.pl line 17.
> >
> >
> > Why does the error only trigger on the second?
> > It's not because it's second - its because *some* things cause the
> > code in
> > toke.c that generates the parsing error not to be reached.
> >
> > Editing the code a bit reveals that the $b *is* being bound to the
> > lexical.
> >
> > It doesn't seem to be based on the class or arity of the builtin -
> > print and
> > sleep do it, endprotoent does not.
> >
> > I have no clue what is going on here.
>
> That code in toke.c is simply horrible. It does a simple scan for <=>
> or cmp anywhere on the same ‘line’. But I don’t fully understand how
> ‘line’ is determined.
>
> $ perl -e 'my $a; sort { ; } $a <=> $b'
> Can't use "my $a" in sort comparison at -e line 1.
>
> $ perl -e 'my $a; sort { ; } $a, "<=>"'
> Can't use "my $a" in sort comparison at -e line 1.
>
> $ perl -e 'my $a; sort { ; } $a, $cmp'
> Can't use "my $a" in sort comparison at -e line 1.
>
> This error has happened to me before, and I found it extremely annoying.
> It should probably be downgraded to a warning.
I’ve downgraded it to a warning and reimplemented it in op.c, so it no
longer gets confused by the presence of the magic sequences ‘cmp’ and ‘<=>’.
By the message still says "my $a", even for state variables. That’s
something I didn’t fix.
The warning is now ‘"my $a" used in sort comparison’.
Should I use "state $a" for state variables, or just say ‘Lexical
variable $a’?
--
Father Chrysostomos
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via perlbug: queue: perl5 status: open
https://rt.perl.org:443/rt3/Ticket/Display.html?id=86136
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