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map{ /.../; { %+ } } @data wrongly flattens hashes into arrays #16519

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p5pRT opened this issue Apr 20, 2018 · 11 comments
Closed

map{ /.../; { %+ } } @data wrongly flattens hashes into arrays #16519

p5pRT opened this issue Apr 20, 2018 · 11 comments

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@p5pRT
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@p5pRT p5pRT commented Apr 20, 2018

Migrated from rt.perl.org#133134 (status was 'rejected')

Searchable as RT133134$

@p5pRT
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@p5pRT p5pRT commented Apr 20, 2018

From @jimav

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 dankogai/p5-encode#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

@p5pRT
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@p5pRT p5pRT commented Apr 20, 2018

From @jimav

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.

@p5pRT
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@p5pRT p5pRT commented Apr 21, 2018

From @jkeenan

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. )

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)

@p5pRT
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@p5pRT p5pRT commented Apr 21, 2018

From @jkeenan

133134.tar.gz

@p5pRT
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@p5pRT p5pRT commented Apr 21, 2018

The RT System itself - Status changed from 'new' to 'open'

@p5pRT
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@p5pRT p5pRT commented Apr 21, 2018

From @iabyn

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-archive.perl.org/perl5/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.)

@p5pRT
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@p5pRT p5pRT commented Apr 21, 2018

From @ilmari

"James E Keenan via RT" <perlbug-followup@​perl.org> writes​:

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. )
[…]
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.

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.

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

@p5pRT
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@p5pRT p5pRT commented Apr 21, 2018

From @xsawyerx

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-archive.perl.org/perl5/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&#8203;: a hash ref constructor
sub f3 \{ 1; \{1;  %a \} \}      \# unambiguous&#8203;: 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

@p5pRT p5pRT closed this as completed Apr 21, 2018
@p5pRT
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@p5pRT p5pRT commented Apr 21, 2018

@iabyn - Status changed from 'open' to 'rejected'

@p5pRT
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@p5pRT p5pRT commented Apr 23, 2018

From @demerphq

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-archive.perl.org/perl5/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&#8203;: a hash ref constructor
sub f3 \{ 1; \{1;  %a \} \}      \# unambiguous&#8203;: a block

Also​:

sub f3 \{ 1; \{; %a \} \}

I picked up the following pattern from rjbs​:

Really? I call that the abigail pattern. :-)

map \+\{ 'key' => 'value' \}\, @&#8203;values; \# hashref expression
map \+\( 'key' => 'value' \)\, @&#8203;values; \# hash expression
map \{; \.\.\. \} @&#8203;values; \# code block

Yep. Parens also has the same effect iirc.

cheers,
Yves

--
perl -Mre=debug -e "/just|another|perl|hacker/"

@p5pRT
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@p5pRT p5pRT commented Apr 23, 2018

From @xsawyerx

On 04/23/2018 10​:06 AM, demerphq wrote​:

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-archive.perl.org/perl5/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&#8203;: a hash ref constructor
sub f3 \{ 1; \{1;  %a \} \}      \# unambiguous&#8203;: 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. :)

map \+\{ 'key' => 'value' \}\, @&#8203;values; \# hashref expression
map \+\( 'key' => 'value' \)\, @&#8203;values; \# hash expression
map \{; \.\.\. \} @&#8203;values; \# code block

Yep. Parens also has the same effect iirc.

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