List::Util attaching to the wrong $_ when used inside given/when construct #9798
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From vparseval@gmail.comCreated by vparseval@gmail.comPlease behold the following: #!/usr/bin/perl -l use feature qw/switch/; my $val = 1; # my $_ Note that when commenting out the lexical declaration of $_, the code behaves At this point, I am not sure if the problem is in List::Util or the perl core. Cheers, Perl Info |
From p5p@perl.wizbit.be
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No it doesn't. Or at least not for me. I suggest you check your test This seem to happen because given creates a lexical $_. It also #!/usr/bin/perl -l use strict; sub s1 (&) { print "Given/when block:"; print ""; print ""; $ perl-5.10.0 rt-67694.pl For loop For loop with lexical $_ Best regards, Bram |
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The RT System itself - Status changed from 'new' to 'open' |
From @rgs2009/7/21 Bram <p5p@perl.wizbit.be>:
Hmm what ? No, given does not create a lexical $_ : from pp_entergiven : if (PL_op->op_targ == 0) { (rewriting that with the proper macros will be nice) (not sure if What happens, at first glance, it that List::Util always uses the We provide UNDERBAR and dUNDERBAR macros to access the current $_, be However we don't have (yet) an API to localize the current $_ as I suppose that code from pp_grepstart could be copied in List::Util to |
From p5p@perl.wizbit.beCiteren Rafael Garcia-Suarez <rgarciasuarez@gmail.com>:
I didn't look at the code only at the docs and the output :/ from perldoc perlsyn: the output shows a different reference for $_ in the when block and in
Then what does in create in pp_entergiven? Adding an our $_ does solve the problem: Given/when block: But why is this be nessesary?
That would only work for the XS version right? Best regards, Bram |
From @rgs2009/7/21 Bram <p5p@perl.wizbit.be>:
Ah, you're right. The parser has this line :
Yes. |
From @iabynOn Tue, Jul 21, 2009 at 12:45:04PM +0200, Rafael Garcia-Suarez wrote:
So if I've understood this correctly, given() adds a lexical $_ to the use List::Util qw/first/; outputs: ok outside -- |
From p5p@perl.wizbit.beCiteren Dave Mitchell <davem@iabyn.com>:
I'm not sure if 'bug' is the correct word. What happens: (example with for instead of given) #!/usr/bin/perl -l for my $_ (1) { sub foo { $c is a closure and closes over $_. But: the closure closes over $_ so it will always uses the value 1... There are, as fas as I can see, two solutions: 1) modify given() so it doesn't use a lexical $_. 2) update the documentation for given() and make it more explicit that Best regards, Bram |
From @iabynOn Fri, Jul 24, 2009 at 07:16:17PM +0200, Bram wrote:
Well, use List::Util qw/first/; outputs ok grep So, the behaviour of first() could be described as unexpected, to say the -- |
From @rgs2009/7/24 Dave Mitchell wrote:
Yes, although I'm not 100% sure that pp_given does exactly the right -- |
From @rgs2009/7/24 Rafael Garcia-Suarez <rgarciasuarez@gmail.com>:
Yes, the patch below solves your reduced test case, the one with grep Graham, would you consider an improved version of the patch below for --- a/ext/List-Util/ListUtil.xs if(items <= 1) { for(index = 1 ; index < items ; index++) { |
From @ikegamiOn Fri, Jul 24, 2009 at 4:42 PM, Rafael Garcia-Suarez <
How are the Pure Perl implementation of List::Util and countless other Perl |
From @ysthOn Fri, July 24, 2009 3:44 pm, Eric Brine wrote:
Add a reference to the proper $_ to the caller() return list? |
From @gbarrOn Jul 24, 2009, at 4:10 PM, Rafael Garcia-Suarez wrote:
Sure. first is the only place in List::Util where $_ is used. This Although should the code passed to first call a sub, that code will Graham.
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From @ysthOn Fri, July 24, 2009 5:28 pm, Yitzchak Scott-Thoennes wrote:
Err, never mind, that wouldn't tell you what $_ was in scope of the sub if |
From fany@cpan.orgCreated by fany@cpan.orgWhen I use a function which expects a codeblock as first Or, in other words, the test script below will output the 1 - 2 - 3 - grep OK! Kind regards, - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - #!/usr/bin/perl -w use 5.01; sub fpp(&@) { my @array = 1 .. 3; my $where = ''; $where = ' within given'; Perl Info |
From @cpansproutOn Sat Dec 10 09:55:36 2011, fany@cpan.org wrote:
This is a known issue, #67694. given does an implicit ‘my $_’. See RJBS: Would you be adverse to changing ‘given’ to alias $_ properly, or -- Father Chrysostomos |
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The RT System itself - Status changed from 'new' to 'open' |
From @cpansproutOn Sat Dec 10 11:51:52 2011, sprout wrote:
BTW, the easiest workaround is to use ‘for’ instead of ‘given’. You can -- Father Chrysostomos |
From [Unknown Contact. See original ticket]On Sat Dec 10 11:51:52 2011, sprout wrote:
BTW, the easiest workaround is to use ‘for’ instead of ‘given’. You can -- Father Chrysostomos |
From tchrist@perl.com"Father Chrysostomos via RT" <perlbug-followup@perl.org> wrote
I've always felt this to be a bug, and would like to see some way --tom |
From @LeontOn Sat, Dec 10, 2011 at 9:04 PM, Tom Christiansen <tchrist@perl.com> wrote:
I'm afraid the only solution is «use 5.016;» :-| Leon |
From @cpansproutOn Sat Dec 10 12:04:57 2011, tom christiansen wrote:
Use powdered eggs. :-) -- Father Chrysostomos |
From @cpansproutOn Sat Dec 10 12:10:19 2011, LeonT wrote:
There is this comment in feature.pm: # TODO: I think that approach would cause too much confusion. feature.pm deals -- Father Chrysostomos |
From @rjbs* Father Chrysostomos via RT <perlbug-followup@perl.org> [2011-12-10T14:51:53]
I agree, *strenuously* that 'given' is a big problem on several fronts, and the I think fixing it via something like :5.16 containing given5_16 is not nuts, In the meantime, would we want to consider warning on closing over lexical $_ This email did not get a lot of deep thought. I composed it during a brief -- |
From @doyOn Sat, Dec 10, 2011 at 06:41:41PM -0500, Ricardo Signes wrote:
+1. I also don't think it's worth trying to reintroduce new semantics
Probably +1, although I haven't given it much thought yet. -doy |
From @cpansproutOn Sat Dec 10 15:42:18 2011, perl.p5p@rjbs.manxome.org wrote:
From a maintenance standpoint, +1000! But I am loath to break anyone’s
Absolutely.
I doubt it. -- Father Chrysostomos |
From @xdgOn Sat, Dec 10, 2011 at 6:41 PM, Ricardo Signes
I'm supportive only if we replaced it with a decent switch construct
A warning sounds reasonable and anyone doing it on purpose can turn -- David |
From chris@prather.orgI missed the list (my apologies David). -Chris ---------- Forwarded message ---------- On Sat, Dec 10, 2011 at 7:52 PM, David Golden <xdaveg@gmail.com> wrote:
Switch and Smart Matching are not equivalent. I'm guessing (hoping?) that Ric is simply talking about deprecating for ($var) { That is all you need for switch is a topicalizer (for) and a test that Fact is that I try very hard to only use given/when in cases where I
no warnings "given"; # none 'expected'; :) -Chris |
From @LeontOn Sun, Dec 11, 2011 at 12:41 AM, Ricardo Signes
It's possible to do the right thing AFAIK, it's just that no one does Leon |
From @cpansproutOn Sun Dec 11 06:05:24 2011, LeonT wrote:
What’s so ironic is that, if called functions can see it, $_ isn’t -- Father Chrysostomos |
From @rjbs* Father Chrysostomos via RT <perlbug-followup@perl.org> [2011-12-11T09:48:24]
given ($x) { Something along those lines?
Well, they're seeing it because they closed over it, right? That's still -- |
From @cpansproutOn Mon Dec 12 12:20:53 2011, perl.p5p@rjbs.manxome.org wrote:
I think Leon Timmermans meant that functions like Scalar::Util::first given ($x) {
I’m referring to the ability of XS modules (like Scalar::Util::first) to -- Father Chrysostomos |
From @LeontOn Mon, Dec 12, 2011 at 10:03 PM, Father Chrysostomos via RT
Exactly.
Though I'm not sure any module uses it currently TBH, ppport and some Leon |
From @cpansproutFixed by b5a6481. |
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@cpansprout - Status changed from 'open' to 'resolved' |
Migrated from rt.perl.org#67694 (status was 'resolved')
Searchable as RT67694$
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