Infinite loop 'while( each { 1=>'a' } )' #14706
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From @KES777This is a bug report for perl from kes-kes@yandex.ru, #!/usr/bin/perl use Modern::Perl; my $val = { 1 => 'a' }; #test 1 OK #test 2 OK (Why this work if "Type of argument to each on reference must be unblessed hashref or arrayref at ./test.pl line 18." #test 3 FAIL not Expected #test4 OK as Expected (see perldoc each) #test 5 FAIL not expected (infinite loop) #test 6 FAIL not Expected (infinite loop) __END__ May you tell me please where I can view status of this BUG report? Flags: Site configuration information for perl 5.18.2: Configured by Debian Project at Thu Mar 27 18:28:21 UTC 2014. Summary of my perl5 (revision 5 version 18 subversion 2) configuration: Locally applied patches: @INC for perl 5.18.2: Environment for perl 5.18.2: |
From @KES777Subject: Infinite loop 'while( each { 1=>'a' } ) This is a bug report for perl from kes-kes@yandex.ru, #!/usr/bin/perl use Modern::Perl; my $val = { 1 => 'a' }; #test 1 OK #test 2 OK (Why this work if "Type of argument to each on reference must be unblessed hashref or arrayref at ./test.pl line 18." #test 3 FAIL not Expected #test4 OK as Expected (see perldoc each) #test 5 FAIL not expected (infinite loop) #test 6 FAIL not Expected (infinite loop) __END__ May you tell me please where I can view status of this BUG report? Configured by Debian Project at Thu Mar 27 18:28:21 UTC 2014. Summary of my perl5 (revision 5 version 18 subversion 2) configuration: Locally applied patches: --- --- |
From @jkeenanOn Sat May 16 00:56:18 2015, kes-kes@yandex.ua wrote:
To report a possible error in Perl itself, you should submit the bug report in a manner in which other possible causes of the error are excluded. Modern::Perl is a library which, if I recall correctly, tries to provide a lot of functionality which has become popular among Perl programmers in the last decade, but it is nonetheless a library which might handle situations differently from Perl itself. So, for the balance of my response, I'm going to proceed as if you had *not* said 'use Modern::Perl'. But I will assume at least Perl 5.18.2 -- the version from which you are filing this bug report -- and I will assume 'use strict;' and 'use warnings;'.
This first gets a warning and then a failure message: Type of argument to each on reference must be unblessed hashref or arrayref at 125205.pl line 18. See: 'perldoc -f each'. The way you are using 'each' above is neither on a hash nor on an array but on its third, experimental version: "a scalar EXPR, which must hold reference to an unblessed hash or array." Your expression does not hold a reference; hence the error.
Since I have to go AFK now, I'll leave analysis of these two cases to others. Thank you very much. -- |
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The RT System itself - Status changed from 'new' to 'open' |
From [email protected]kes-kes@yandex.ua wrote:
It works because this isn't "each on reference". It's the old-style
This creates a fresh hash each time round the loop, via the {} constructor
Same again, this time using each on the reference. -zefram |
From @demerphqOn 16 May 2015 at 09:56, KES <perlbug-followup@perl.org> wrote:
As far as I can tell, and I think Zefram agrees, this is not a bug. Yves |
From @kentfredric
At best, one could potentially submit documentation for perlfunc/each to -- *KENTNL* - https://metacpan.org/author/KENTNL |
From @jkeenanSince this is not a bug in Perl, I am taking the ticket for the purpose of closing it within 7 days unless there is further discussion. -- |
From @KES777
I do not agree with you. for( keys { 1 => 'a', 2 => 'b' } ) { As you say this must also creates a fresh hash, but it does not.
Becase 'each' access internal iterator of hash in same manner as 'keys'/'values' do. You can use this iterator. 1. What is the benifit of recalculating argument of 'each' for every 'while' iteration? 2. Does this broken in compare to 5.12? print shift split ' ', '1 2'; 3. Can I force hash for ( 1 => 'a', 2 => 'b' ) without temporary variable? maybe like: or force to not calculate 'each's EXPR on 'while' iterations: |
From [email protected]KES wrote:
Different case. A while loop evaluates its conditional expression each
It creates a fresh hash once per execution of the whole foreach loop.
That's what it does, wasteful or not. Except that technically we don't
This refers to the well-known side effect that the keys and values You can see this resetting effect by comparing these two loops: $ perl -lwe '%a=(a=>1,b=>2,c=>3); while ($_ = each %a) { print $_; }' This means that there is practical utility in that `wasteful' behaviour
The keys operator does all the hash iteration in one go. With the choice
It is fundamental to the while operator that it evaluates the conditional my $h = { 1 => "a", 2 => "b" };
shift is another of the operators to which the experimental implicit
That doesn't quite make sense, because you don't have a hash constructor
is precisely possible, using a module from CPAN: use Memoize::Once qw(once); See also the quite similar Memoize::Lift. However, these operators cause -zefram |
From @KES777Ok, thank you for your explanation. 18.05.2015, 19:37, "Zefram via RT" <perlbug-followup@perl.org>:
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@iabyn - Status changed from 'open' to 'rejected' |
From @ap* KES <kes-kes@yandex.ua> [2015-05-18 19:20]:
No. That would require a combination of several special cases, and that “Any language that doesn't occasionally surprise the novice Now you know how it works. So just store it in a variable and move on. Regards, |
Migrated from rt.perl.org#125205 (status was 'rejected')
Searchable as RT125205$
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