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Id: 133134
Status: rejected
Priority: 0/
Queue: perl5

Owner: Nobody
Requestors: jim.avera [at] gmail.com
Cc:
AdminCc:

Operating System: (no value)
PatchStatus: (no value)
Severity: low
Type: notabug
Perl Version: (no value)
Fixed In: (no value)



From: jim.avera [...] gmail.com
Subject: map{ /.../; { %+ } } @data wrongly flattens hashes into arrays
Date: Fri, 20 Apr 2018 13:25:36 -0700 (PDT)
To: perlbug [...] perl.org
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This is a bug report for perl from jim.avera@gmail.com, generated with the help of perlbug 1.40 running under perl 5.26.1. ----------------------------------------------------------------- If used inside map{...}, the construct { %+ } results in a flat list of keys and values, not a ref to a hash. For example, map{ /^(?<a>A*)(?<b>B*)$/ or die; { %+ } } ("AB", "AABBB", "AAAB"); returns ('a', 'A', 'b', 'B', 'a', 'AA', 'b', 'BBB', 'a', 'AAA', 'b', 'B') instead of ( {'a' => 'A', 'b' => 'B' }, etc. ) A demo script follows. #!/usr/bin/perl use strict; use warnings; use Data::Dumper; my @list1; foreach ("AB", "AABBB", "AAAB") { /^(?<a>A*)(?<b>B*)$/ or die; push @list1, { %+ }; } my @list2 = map{ /^(?<a>A*)(?<b>B*)$/ or die; { a=>$+{a}, b=> $+{b} } } ("AB", "AABBB", "AAAB"); my @list3 = map{ /^(?<a>A*)(?<b>B*)$/ or die; { %+ } } ("AB", "AABBB", "AAAB"); print Data::Dumper->Dump([\@list1,\@list2,\@list3], [qw(list1 list2 list3)]); ----------------------------------------------------------------- --- Flags: category=core severity=low --- Site configuration information for perl 5.26.1: Configured by Ubuntu at Fri Feb 23 15:23:43 UTC 2018. Summary of my perl5 (revision 5 version 26 subversion 1) configuration: Platform: osname=linux osvers=4.9.0 archname=x86_64-linux-gnu-thread-multi uname='linux localhost 4.9.0 #1 smp debian 4.9.0 x86_64 gnulinux ' config_args='-Dusethreads -Duselargefiles -Dcc=x86_64-linux-gnu-gcc -Dcpp=x86_64-linux-gnu-cpp -Dld=x86_64-linux-gnu-gcc -Dccflags=-DDEBIAN -Wdate-time -D_FORTIFY_SOURCE=2 -g -O2 -fdebug-prefix-map=/build/perl-hD18Cr/perl-5.26.1=. -fstack-protector-strong -Wformat -Werror=format-security -Dldflags= -Wl,-Bsymbolic-functions -Wl,-z,relro -Dlddlflags=-shared -Wl,-Bsymbolic-functions -Wl,-z,relro -Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.26 -Darchlib=/usr/lib/x86_64-linux-gnu/perl/5.26 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/x86_64-linux-gnu/perl5/5.26 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.26.1 -Dsitearch=/usr/local/lib/x86_64-linux-gnu/perl/5.26.1 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Duse64bitint -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -Ui_libutil -Ui_xlocale -Uversiononly -DDEBUGGING=-g -Doptimize=-O2 -dEs -Duseshrplib -Dlibperl=libperl.so.5.26.1' hint=recommended useposix=true d_sigaction=define useithreads=define usemultiplicity=define use64bitint=define use64bitall=define uselongdouble=undef usemymalloc=n default_inc_excludes_dot=define bincompat5005=undef Compiler: cc='x86_64-linux-gnu-gcc' ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64' optimize='-O2 -g' cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include' ccversion='' gccversion='7.3.0' gccosandvers='' intsize=4 longsize=8 ptrsize=8 doublesize=8 byteorder=12345678 doublekind=3 d_longlong=define longlongsize=8 d_longdbl=define longdblsize=16 longdblkind=3 ivtype='long' ivsize=8 nvtype='double' nvsize=8 Off_t='off_t' lseeksize=8 alignbytes=8 prototype=define Linker and Libraries: ld='x86_64-linux-gnu-gcc' ldflags =' -fstack-protector-strong -L/usr/local/lib' libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/7/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt perllibs=-ldl -lm -lpthread -lc -lcrypt libc=libc-2.27.so so=so useshrplib=true libperl=libperl.so.5.26 gnulibc_version='2.27' Dynamic Linking: dlsrc=dl_dlopen.xs dlext=so d_dlsymun=undef ccdlflags='-Wl,-E' cccdlflags='-fPIC' lddlflags='-shared -L/usr/local/lib -fstack-protector-strong' Locally applied patches: DEBPKG:debian/cpan_definstalldirs - Provide a sensible INSTALLDIRS default for modules installed from CPAN. DEBPKG:debian/db_file_ver - https://bugs.debian.org/340047 Remove overly restrictive DB_File version check. DEBPKG:debian/doc_info - Replace generic man(1) instructions with Debian-specific information. DEBPKG:debian/enc2xs_inc - https://bugs.debian.org/290336 Tweak enc2xs to follow symlinks and ignore missing @INC directories. DEBPKG:debian/errno_ver - https://bugs.debian.org/343351 Remove Errno version check due to upgrade problems with long-running processes. DEBPKG:debian/libperl_embed_doc - https://bugs.debian.org/186778 Note that libperl-dev package is required for embedded linking DEBPKG:fixes/respect_umask - Respect umask during installation DEBPKG:debian/writable_site_dirs - Set umask approproately for site install directories DEBPKG:debian/extutils_set_libperl_path - EU:MM: set location of libperl.a under /usr/lib DEBPKG:debian/no_packlist_perllocal - Don't install .packlist or perllocal.pod for perl or vendor DEBPKG:debian/fakeroot - Postpone LD_LIBRARY_PATH evaluation to the binary targets. DEBPKG:debian/instmodsh_doc - Debian policy doesn't install .packlist files for core or vendor. DEBPKG:debian/ld_run_path - Remove standard libs from LD_RUN_PATH as per Debian policy. DEBPKG:debian/libnet_config_path - Set location of libnet.cfg to /etc/perl/Net as /usr may not be writable. DEBPKG:debian/perlivp - https://bugs.debian.org/510895 Make perlivp skip include directories in /usr/local DEBPKG:debian/deprecate-with-apt - https://bugs.debian.org/747628 Point users to Debian packages of deprecated core modules DEBPKG:debian/squelch-locale-warnings - https://bugs.debian.org/508764 Squelch locale warnings in Debian package maintainer scripts DEBPKG:debian/patchlevel - https://bugs.debian.org/567489 List packaged patches for 5.26.1-5 in patchlevel.h DEBPKG:fixes/document_makemaker_ccflags - https://bugs.debian.org/628522 [rt.cpan.org #68613] Document that CCFLAGS should include $Config{ccflags} DEBPKG:debian/find_html2text - https://bugs.debian.org/640479 Configure CPAN::Distribution with correct name of html2text DEBPKG:debian/perl5db-x-terminal-emulator.patch - https://bugs.debian.org/668490 Invoke x-terminal-emulator rather than xterm in perl5db.pl DEBPKG:debian/cpan-missing-site-dirs - https://bugs.debian.org/688842 Fix CPAN::FirstTime defaults with nonexisting site dirs if a parent is writable DEBPKG:fixes/memoize_storable_nstore - [rt.cpan.org #77790] https://bugs.debian.org/587650 Memoize::Storable: respect 'nstore' option not respected DEBPKG:debian/makemaker-pasthru - https://bugs.debian.org/758471 Pass LD settings through to subdirectories DEBPKG:debian/makemaker-manext - https://bugs.debian.org/247370 Make EU::MakeMaker honour MANnEXT settings in generated manpage headers DEBPKG:debian/kfreebsd-softupdates - https://bugs.debian.org/796798 Work around Debian Bug#796798 DEBPKG:fixes/autodie-scope - https://bugs.debian.org/798096 Fix a scoping issue with "no autodie" and the "system" sub DEBPKG:fixes/memoize-pod - [rt.cpan.org #89441] Fix POD errors in Memoize DEBPKG:debian/hurd-softupdates - https://bugs.debian.org/822735 Fix t/op/stat.t failures on hurd DEBPKG:fixes/math_complex_doc_great_circle - https://bugs.debian.org/697567 [rt.cpan.org #114104] Math::Trig: clarify definition of great_circle_midpoint DEBPKG:fixes/math_complex_doc_see_also - https://bugs.debian.org/697568 [rt.cpan.org #114105] Math::Trig: add missing SEE ALSO DEBPKG:fixes/math_complex_doc_angle_units - https://bugs.debian.org/731505 [rt.cpan.org #114106] Math::Trig: document angle units DEBPKG:fixes/cpan_web_link - https://bugs.debian.org/367291 CPAN: Add link to main CPAN web site DEBPKG:fixes/time_piece_doc - https://bugs.debian.org/817925 Time::Piece: Improve documentation for add_months and add_years DEBPKG:fixes/extutils_makemaker_reproducible - https://bugs.debian.org/835815 https://bugs.debian.org/834190 Make perllocal.pod files reproducible DEBPKG:fixes/file_path_hurd_errno - File-Path: Fix test failure in Hurd due to hard-coded ENOENT DEBPKG:debian/hppa_op_optimize_workaround - https://bugs.debian.org/838613 Temporarily lower the optimization of op.c on hppa due to gcc-6 problems DEBPKG:debian/installman-utf8 - https://bugs.debian.org/840211 Generate man pages with UTF-8 characters DEBPKG:fixes/file_path_chmod_race - https://bugs.debian.org/863870 [rt.cpan.org #121951] Prevent directory chmod race attack. DEBPKG:fixes/extutils_file_path_compat - Correct the order of tests of chmod(). (#294) DEBPKG:fixes/getopt-long-2 - [rt.cpan.org #120300] Withdraw part of commit 5d9947fb445327c7299d8beb009d609bc70066c0, which tries to implement more GNU getopt_long campatibility. GNU DEBPKG:fixes/getopt-long-3 - provide a default value for optional arguments DEBPKG:fixes/getopt-long-4 - https://bugs.debian.org/864544 [rt.cpan.org #122068] Fix issue #122068. DEBPKG:fixes/test-builder-reset - https://bugs.debian.org/865894 Reset inside subtest maintains parent DEBPKG:debian/hppa_opmini_optimize_workaround - https://bugs.debian.org/869122 Lower the optimization level of opmini.c on hppa DEBPKG:debian/sh4_op_optimize_workaround - https://bugs.debian.org/869373 Also lower the optimization level of op.c and opmini.c on sh4 DEBPKG:fixes/json-pp-example - [rt.cpan.org #92793] https://bugs.debian.org/871837 fix RT-92793: bug in SYNOPSIS DEBPKG:debian/perldoc-pager - https://bugs.debian.org/870340 [rt.cpan.org #120229] Fix perldoc terminal escapes when sensible-pager is less DEBPKG:debian/prune_libs - https://bugs.debian.org/128355 Prune the list of libraries wanted to what we actually need. DEBPKG:debian/configure-regen - https://bugs.debian.org/762638 Regenerate Configure et al. after probe unit changes DEBPKG:fixes/rename-filexp.U-phase1 - regen-configure: rename filexp.U to filexp_path.U, phase 1 DEBPKG:fixes/rename-filexp.U-phase2 - regen-configure: rename filexp.U to filexp_path.U, phase 2 DEBPKG:fixes/packaging_test_skips - Skip various tests if PERL_BUILD_PACKAGING is set DEBPKG:debian/mod_paths - Tweak @INC ordering for Debian DEBPKG:fixes/encode-alias-regexp - https://bugs.debian.org/880085 fix https://github.com/dankogai/p5-encode/issues/127 DEBPKG:fixes/regex-memory-leak - [910a6a8] https://bugs.debian.org/891196 [perl #132892] perl #132892: avoid leak by mortalizing temporary copy of pattern --- @INC for perl 5.26.1: /home/jima/lib/perl /home/jima/perl5/lib/perl5/x86_64-linux-gnu-thread-multi /home/jima/perl5/lib/perl5/x86_64-linux-gnu-thread-multi /home/jima/perl5/lib/perl5 /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.26.1 /usr/local/share/perl/5.26.1 /usr/lib/x86_64-linux-gnu/perl5/5.26 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.26 /usr/share/perl/5.26 /home/jima/perl5/lib/perl5/5.26.0 /home/jima/perl5/lib/perl5/5.26.0/x86_64-linux-gnu-thread-multi /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base --- Environment for perl 5.26.1: HOME=/home/jima LANG=en_US.UTF-8 LANGUAGE (unset) LC_COLLATE=C LD_LIBRARY_PATH (unset) LOGDIR (unset) PATH=/home/jima/.local/bin:/home/jima/perl5/bin:/home/jima/bin:/home/jima/jima_tools/x86_64/bin:/home/jima/jima_tools/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/bin/X11:/usr/local/bin:/usr/local/sbin:/usr/games:/usr/local/games:/snap/bin:/usr/lib/jvm/java-8-oracle/bin:/usr/lib/jvm/java-8-oracle/db/bin:/usr/lib/jvm/java-8-oracle/jre/bin:. PERL5LIB=/home/jima/lib/perl:/home/jima/perl5/lib/perl5/x86_64-linux-gnu-thread-multi:/home/jima/perl5/lib/perl5 PERL_BADLANG (unset) PERL_LOCAL_LIB_ROOT=/home/jima/perl5 PERL_MB_OPT=--install_base /home/jima/perl5 PERL_MM_OPT=INSTALL_BASE=/home/jima/perl5 SHELL=/bin/bash
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Show quoted text
> map{ /.../; { %+ } } @data > returns a flat list instead of list of hashrefs
Okay, this seems to be because the compiler thinks { %+ } is just a nested block, not a hashref constructor. Adding parens fixes the problem: map{ /.../; ( {%+} ) } @data returns a list of hashrefs as expected. Sorry for the noise.
RT-Send-CC: perl5-porters [...] perl.org
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On Fri, 20 Apr 2018 20:25:49 GMT, jim.avera@gmail.com wrote: Show quoted text
> > This is a bug report for perl from jim.avera@gmail.com, > generated with the help of perlbug 1.40 running under perl 5.26.1. > > ----------------------------------------------------------------- > If used inside map{...}, the construct > > { %+ } > > results in a flat list of keys and values, not a ref to a hash. > For example, > > map{ /^(?<a>A*)(?<b>B*)$/ or die; { %+ } } ("AB", "AABBB", "AAAB"); > > returns > > ('a', 'A', 'b', 'B', 'a', 'AA', 'b', 'BBB', 'a', 'AAA', 'b', 'B') > > instead of > > ( {'a' => 'A', 'b' => 'B' }, etc. ) > > A demo script follows. > > #!/usr/bin/perl > use strict; use warnings; > use Data::Dumper; > > my @list1; > foreach ("AB", "AABBB", "AAAB") { > /^(?<a>A*)(?<b>B*)$/ or die; > push @list1, { %+ }; > } > my @list2 = map{ /^(?<a>A*)(?<b>B*)$/ or die; { a=>$+{a}, b=> $+{b} } > } > ("AB", "AABBB", "AAAB"); > my @list3 = map{ /^(?<a>A*)(?<b>B*)$/ or die; { %+ } } > ("AB", "AABBB", "AAAB"); > > print Data::Dumper->Dump([\@list1,\@list2,\@list3], [qw(list1 list2 > list3)]); > >
Using perlbrew, I checked out various production releases of perl, ran your program in each and recorded the results. See attachment. The program wouldn't compile in 5.8.9, but did in 5.10.1. From 5.10.1 the result was stable up through 5.16.3. As of 5.18.4 the results differ each release. (I haven't looked closely enough to see whether or not this is just reshuffling of hash elements.) So this does not appear to be a regression appearing for the first time in the 5.27 dev cycle. Thank you very much. -- James E Keenan (jkeenan@cpan.org)
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Subject: Re: [perl #133134] map{ /.../; { %+ } } @data wrongly flattens hashes into arrays
From: Dave Mitchell <davem [...] iabyn.com>
To: perl5-porters [...] perl.org
Date: Sat, 21 Apr 2018 09:28:42 +0100
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On Fri, Apr 20, 2018 at 01:25:49PM -0700, via RT wrote: Show quoted text
> # New Ticket Created by > # Please include the string: [perl #133134] > # in the subject line of all future correspondence about this issue. > # <URL: https://rt.perl.org/Ticket/Display.html?id=133134 > > > > > This is a bug report for perl from jim.avera@gmail.com, > generated with the help of perlbug 1.40 running under perl 5.26.1. > > ----------------------------------------------------------------- > If used inside map{...}, the construct > > { %+ } > > results in a flat list of keys and values, not a ref to a hash.
An '{' at the start of a statement is ambiguous: it could be the start of a new block, or the start of a hash constructor. In this situation, perl makes an educated guess based on the first few characters following the '{'. In this case, its guess didn't match your hopes. You can avoid the ambiguity by providing perl with more information; for example: %a = qw(a 1 b 2); sub f1 { 1; { %a } } # ambiguous sub f2 { 1; scalar { %a } } # unambiguous: a hash ref constructor sub f3 { 1; {1; %a } } # unambiguous: a block print ((f1())[0], "\n"); print ((f2())[0], "\n"); print ((f3())[0], "\n"); which outputs: a HASH(0x22314e8) a -- "I used to be with it, but then they changed what ‘it’ was, and now what I’m with isn’t it. And what’s ‘it’ seems weird and scary to me." -- Grandpa Simpson (It will happen to you too.)
Date: Sat, 21 Apr 2018 09:30:56 +0100
From: ilmari [...] ilmari.org (Dagfinn Ilmari Mannsåker)
Subject: Re: [perl #133134] map{ /.../; { %+ } } @data wrongly flattens hashes into arrays
To: perlbug-followup [...] perl.org
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"James E Keenan via RT" <perlbug-followup@perl.org> writes: Show quoted text
> On Fri, 20 Apr 2018 20:25:49 GMT, jim.avera@gmail.com wrote:
>> >> This is a bug report for perl from jim.avera@gmail.com, >> generated with the help of perlbug 1.40 running under perl 5.26.1. >> >> ----------------------------------------------------------------- >> If used inside map{...}, the construct >> >> { %+ } >> >> results in a flat list of keys and values, not a ref to a hash. >> For example, >> >> map{ /^(?<a>A*)(?<b>B*)$/ or die; { %+ } } ("AB", "AABBB", "AAAB"); >> >> returns >> >> ('a', 'A', 'b', 'B', 'a', 'AA', 'b', 'BBB', 'a', 'AAA', 'b', 'B') >> >> instead of >> >> ( {'a' => 'A', 'b' => 'B' }, etc. )
[…] Show quoted text
> Using perlbrew, I checked out various production releases of perl, ran > your program in each and recorded the results. See attachment. > > The program wouldn't compile in 5.8.9, but did in 5.10.1.
This is because the regex uses named captures, which were introduced in 5.10. Show quoted text
> From 5.10.1 the result was stable up through 5.16.3. As of 5.18.4 the > results differ each release. (I haven't looked closely enough to see > whether or not this is just reshuffling of hash elements.)
This is because %+ is a hash, and hash order is randomised since 5.18. Show quoted text
> So this does not appear to be a regression appearing for the first > time in the 5.27 dev cycle.
It is not a bug at all. The reason is that the { %+ } gets interpreted as a block statement, rather than a hashref constructor expression. The standard way to disambiguate it to an expression is to precede it with a unary +: $ perl -MDevel::Dwarn -e 'Dwarn([map{ /^(?<a>A*)(?<b>B*)$/ or die; +{ %+ } } ("AB")])' [ { a => "A", b => "B", }, ] This ticket should be closed. - ilmari -- "The surreality of the universe tends towards a maximum" -- Skud's Law "Never formulate a law or axiom that you're not prepared to live with the consequences of." -- Skud's Meta-Law
To: perl5-porters [...] perl.org
From: Sawyer X <xsawyerx [...] gmail.com>
Subject: Re: [perl #133134] map{ /.../; { %+ } } @data wrongly flattens hashes into arrays
Date: Sat, 21 Apr 2018 10:33:28 +0200
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On 04/21/2018 10:28 AM, Dave Mitchell wrote: Show quoted text
> On Fri, Apr 20, 2018 at 01:25:49PM -0700, via RT wrote:
>> # New Ticket Created by >> # Please include the string: [perl #133134] >> # in the subject line of all future correspondence about this issue. >> # <URL: https://rt.perl.org/Ticket/Display.html?id=133134 > >> >> >> >> This is a bug report for perl from jim.avera@gmail.com, >> generated with the help of perlbug 1.40 running under perl 5.26.1. >> >> ----------------------------------------------------------------- >> If used inside map{...}, the construct >> >> { %+ } >> >> results in a flat list of keys and values, not a ref to a hash.
> An '{' at the start of a statement is ambiguous: it could be the start > of a new block, or the start of a hash constructor. In this situation, perl > makes an educated guess based on the first few characters following the > '{'. In this case, its guess didn't match your hopes. > > You can avoid the ambiguity by providing perl with more information; for > example: > > %a = qw(a 1 b 2); > > sub f1 { 1; { %a } } # ambiguous > sub f2 { 1; scalar { %a } } # unambiguous: a hash ref constructor > sub f3 { 1; {1; %a } } # unambiguous: a block
Also: sub f3 { 1; {; %a } } I picked up the following pattern from rjbs: map +{ 'key' => 'value' }, @values; # hashref expression map +( 'key' => 'value' ), @values; # hash expression map {; ... } @values; # code block
CC: Perl5 Porteros <perl5-porters [...] perl.org>
Subject: Re: [perl #133134] map{ /.../; { %+ } } @data wrongly flattens hashes into arrays
From: demerphq <demerphq [...] gmail.com>
To: Sawyer X <xsawyerx [...] gmail.com>
Date: Mon, 23 Apr 2018 10:06:10 +0200
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On 21 April 2018 at 10:33, Sawyer X <xsawyerx@gmail.com> wrote: Show quoted text
> > > On 04/21/2018 10:28 AM, Dave Mitchell wrote:
>> On Fri, Apr 20, 2018 at 01:25:49PM -0700, via RT wrote:
>>> # New Ticket Created by >>> # Please include the string: [perl #133134] >>> # in the subject line of all future correspondence about this issue. >>> # <URL: https://rt.perl.org/Ticket/Display.html?id=133134 > >>> >>> >>> >>> This is a bug report for perl from jim.avera@gmail.com, >>> generated with the help of perlbug 1.40 running under perl 5.26.1. >>> >>> ----------------------------------------------------------------- >>> If used inside map{...}, the construct >>> >>> { %+ } >>> >>> results in a flat list of keys and values, not a ref to a hash.
>> An '{' at the start of a statement is ambiguous: it could be the start >> of a new block, or the start of a hash constructor. In this situation, perl >> makes an educated guess based on the first few characters following the >> '{'. In this case, its guess didn't match your hopes. >> >> You can avoid the ambiguity by providing perl with more information; for >> example: >> >> %a = qw(a 1 b 2); >> >> sub f1 { 1; { %a } } # ambiguous >> sub f2 { 1; scalar { %a } } # unambiguous: a hash ref constructor >> sub f3 { 1; {1; %a } } # unambiguous: a block
> > Also: > > sub f3 { 1; {; %a } } > > I picked up the following pattern from rjbs:
Really? I call that the abigail pattern. :-) Show quoted text
> map +{ 'key' => 'value' }, @values; # hashref expression > map +( 'key' => 'value' ), @values; # hash expression > map {; ... } @values; # code block
Yep. Parens also has the same effect iirc. cheers, Yves -- perl -Mre=debug -e "/just|another|perl|hacker/"
CC: Perl5 Porteros <perl5-porters [...] perl.org>
Subject: Re: [perl #133134] map{ /.../; { %+ } } @data wrongly flattens hashes into arrays
From: Sawyer X <xsawyerx [...] gmail.com>
To: demerphq <demerphq [...] gmail.com>
Date: Mon, 23 Apr 2018 10:34:03 +0200
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On 04/23/2018 10:06 AM, demerphq wrote: Show quoted text
> On 21 April 2018 at 10:33, Sawyer X <xsawyerx@gmail.com> wrote:
>> >> On 04/21/2018 10:28 AM, Dave Mitchell wrote:
>>> On Fri, Apr 20, 2018 at 01:25:49PM -0700, via RT wrote:
>>>> # New Ticket Created by >>>> # Please include the string: [perl #133134] >>>> # in the subject line of all future correspondence about this issue. >>>> # <URL: https://rt.perl.org/Ticket/Display.html?id=133134 > >>>> >>>> >>>> >>>> This is a bug report for perl from jim.avera@gmail.com, >>>> generated with the help of perlbug 1.40 running under perl 5.26.1. >>>> >>>> ----------------------------------------------------------------- >>>> If used inside map{...}, the construct >>>> >>>> { %+ } >>>> >>>> results in a flat list of keys and values, not a ref to a hash.
>>> An '{' at the start of a statement is ambiguous: it could be the start >>> of a new block, or the start of a hash constructor. In this situation, perl >>> makes an educated guess based on the first few characters following the >>> '{'. In this case, its guess didn't match your hopes. >>> >>> You can avoid the ambiguity by providing perl with more information; for >>> example: >>> >>> %a = qw(a 1 b 2); >>> >>> sub f1 { 1; { %a } } # ambiguous >>> sub f2 { 1; scalar { %a } } # unambiguous: a hash ref constructor >>> sub f3 { 1; {1; %a } } # unambiguous: a block
>> Also: >> >> sub f3 { 1; {; %a } } >> >> I picked up the following pattern from rjbs:
> Really? I call that the abigail pattern. :-)
I wouldn't be surprised to learn this is where rjbs got it. :) Show quoted text
>
>> map +{ 'key' => 'value' }, @values; # hashref expression >> map +( 'key' => 'value' ), @values; # hash expression >> map {; ... } @values; # code block
> Yep. Parens also has the same effect iirc.


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