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attributes affect listiness of declarations #16220

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p5pRT opened this issue Nov 3, 2017 · 1 comment
Open

attributes affect listiness of declarations #16220

p5pRT opened this issue Nov 3, 2017 · 1 comment

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@p5pRT
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p5pRT commented Nov 3, 2017

Migrated from rt.perl.org#132393 (status was 'new')

Searchable as RT132393$

@p5pRT
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p5pRT commented Nov 3, 2017

From zefram@fysh.org

Created by zefram@fysh.org

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".

Perl Info

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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