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Report information
Id: 132393
Status: new
Priority: 0/
Queue: perl5

Owner: Nobody
Requestors: zefram [at] fysh.org
Cc:
AdminCc:

Operating System: (no value)
PatchStatus: (no value)
Severity: medium
Type: core
Perl Version: 5.27.5
Fixed In: (no value)



Subject: attributes affect listiness of declarations
From: zefram [...] fysh.org
Date: Fri, 03 Nov 2017 21:46:44 +0000
CC: zefram [...] fysh.org
To: perlbug [...] perl.org
This is a bug report for perl from zefram@fysh.org, generated with the help of perlbug 1.40 running under perl 5.27.5. ----------------------------------------------------------------- [Please describe your issue here] A "my" declaration of a scalar variable, with no parens, is a scalar for the purposes of determining assignment type: $ perl -lwe '@p = qw(x y z); my $a = @p; print $a' 3 If it's enclosed in parens, that makes a list for the purposes of assignment: $ perl -lwe '@p = qw(x y z); (my $a) = @p; print $a' x But if the declaration also includes an attribute, then the parenthesised list becomes a scalar: $ perl -lwe '@p = qw(x y z); (my $a :shared) = @p; print $a' 3 That looks like a bug to me. Note that it's possible to have a scalar assignment to attributeful "my" declaration without any parens: $ perl -lwe '@p = qw(x y z); my $a :shared = @p; print $a' 3 Also, the scalarness isn't strictly driven by the use of attribute syntax, as one might expect. If attribute syntax is invoked by the use of ":" but no actual attribute is supplied, then the parenthesised list remains a list: $ perl -lwe '@p = qw(x y z); (my $a :) = @p; print $a' x This bug has some effect on [perl #114932], in that "(state $a :shared) =", which looks like a list-mode assignment which would be currently forbidden, is treated as a scalar initialisation. Not only is it permitted, but it also gets the one-time-initialisation semantic that the parens around the declaration ought to suppress: $ perl -Mfeature=state -lwe '@p = qw(x y z); sub f { (state $a :shared) = @p; print $a; } f(); unshift @p, "w"; f()' 3 3 Although I found this while investigating [perl #114932], and it has some effect on it, this is not really part of that issue. As the matching "my" cases show, this is a semantic problem that exists independent of "state". [Please do not change anything below this line] ----------------------------------------------------------------- --- Flags: category=core severity=medium --- Site configuration information for perl 5.27.5: Configured by zefram at Fri Oct 20 23:24:00 BST 2017. Summary of my perl5 (revision 5 version 27 subversion 5) configuration: Platform: osname=linux osvers=3.16.0-4-amd64 archname=x86_64-linux-thread-multi uname='linux barba.rous.org 3.16.0-4-amd64 #1 smp debian 3.16.43-2+deb8u2 (2017-06-26) x86_64 gnulinux ' config_args='-des -Dprefix=/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52 -Duselargefiles -Dusethreads -Uafs -Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dusedevel -Uversiononly -Ui_db' 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='cc' ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2' optimize='-O2' cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include' ccversion='' gccversion='4.9.2' 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='cc' ldflags =' -fstack-protector-strong -L/usr/local/lib' libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.9/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=-lpthread -lnsl -ldb -ldl -lm -lcrypt -lutil -lc perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc libc=libc-2.19.so so=so useshrplib=true libperl=libperl.so gnulibc_version='2.19' Dynamic Linking: dlsrc=dl_dlopen.xs dlext=so d_dlsymun=undef ccdlflags='-Wl,-E -Wl,-rpath,/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5/x86_64-linux-thread-multi/CORE' cccdlflags='-fPIC' lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong' --- @INC for perl 5.27.5: /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/site_perl/5.27.5/x86_64-linux-thread-multi /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/site_perl/5.27.5 /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5/x86_64-linux-thread-multi /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5 --- Environment for perl 5.27.5: HOME=/home/zefram LANG (unset) LANGUAGE (unset) LD_LIBRARY_PATH (unset) LOGDIR (unset) PATH=/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/bin:/home/zefram/usr/perl/util:/home/zefram/pub/x86_64-unknown-linux-gnu/bin:/home/zefram/pub/common/bin:/usr/bin:/bin:/usr/local/bin:/usr/games PERLDOC=-oman PERL_BADLANG (unset) SHELL=/usr/bin/zsh


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