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[perl #132776] lvalue+signature example: should not return read-onlyvalue

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From:
slaven @ rezic . de
Date:
January 28, 2018 09:39
Subject:
[perl #132776] lvalue+signature example: should not return read-onlyvalue
Message ID:
rt-4.0.24-25005-1517132353-744.132776-75-0@perl.org
# New Ticket Created by  slaven@rezic.de 
# Please include the string:  [perl #132776]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=132776 >



This is a bug report for perl from slaven@rezic.de,
generated with the help of perlbug 1.41 running under perl 5.27.8.


-----------------------------------------------------------------
A minor nit in perl5.27.8's perldelta.pod: the two examples

	sub f :lvalue ($a, $b) { 1 }; # 5.20; 5.28 onwards
	sub f ($a, $b) :lvalue { 1 }; # 5.22 - 5.26

don't work because a read-only value is returned. A complete test script:

#!/usr/bin/perl
use strict;
use feature 'signatures';
no warnings 'experimental';
sub f :lvalue ($a, $b) { 1 };
f(1,2) = 123;
__END__

Output is:

Can't return a readonly value from lvalue subroutine at signatures.pl line 5.

Probably using a variable here would be better.

-----------------------------------------------------------------
---
Flags:
    category=docs
    severity=low
---
Site configuration information for perl 5.27.8:

Configured by eserte at Sat Jan 20 09:22:10 CET 2018.

Summary of my perl5 (revision 5 version 27 subversion 8) configuration:
   
  Platform:
    osname=linux
    osvers=3.16.0-4-amd64
    archname=x86_64-linux
    uname='linux cabulja 3.16.0-4-amd64 #1 smp debian 3.16.51-3 (2017-12-13) x86_64 gnulinux '
    config_args='-ds -e -Dprefix=/opt/perl-5.27.8 -Dusedevel -Dusemallocwrap=no -Dcf_email=srezic@cpan.org'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
    bincompat5005=undef
  Compiler:
    cc='cc'
    ccflags ='-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='-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 -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.19.so
    so=so
    useshrplib=false
    libperl=libperl.a
    gnulibc_version='2.19'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'


---
@INC for perl 5.27.8:
    /opt/perl-5.27.8/lib/site_perl/5.27.8/x86_64-linux
    /opt/perl-5.27.8/lib/site_perl/5.27.8
    /opt/perl-5.27.8/lib/5.27.8/x86_64-linux
    /opt/perl-5.27.8/lib/5.27.8

---
Environment for perl 5.27.8:
    HOME=/home/eserte
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/home/eserte/bin/linux-gnu:/home/eserte/bin/sh:/home/eserte/bin:/home/eserte/bin/pistachio-perl/bin:/usr/games:/home/eserte/devel
    PERLDOC=-MPod::Perldoc::ToTextOverstrike
    PERL_BADLANG (unset)
    SHELL=/bin/zsh


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