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[perl #120863] foreach on hash keys should give readonly scalar
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From:
Ed Avis
Date:
December 24, 2013 12:34
Subject:
[perl #120863] foreach on hash keys should give readonly scalar
Message ID:
rt-4.0.18-30850-1387888470-778.120863-75-0@perl.org
# New Ticket Created by "Ed Avis"
# Please include the string: [perl #120863]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org/Ticket/Display.html?id=120863 >
This is a bug report for perl from eda@waniasset.com,
generated with the help of perlbug 1.39 running under perl 5.16.3.
-----------------------------------------------------------------
[Please describe your issue here]
In a C<foreach> loop the loop variable is an alias to the entries of
the list being iterated over. That means you can modify the variable
inside the loop and, if iterating over an array or something else
lvalue-ish, you can change the array's values.
When iterating over C<keys %h> you can also write to the loop
variable, but the changes do not propagate back to the hash. It would
be better to make the loop variable a read-only scalar in this case.
Indeed, perhaps it should be read-only in all cases where the original
values can't be changed. But that might be a drastic change breaking
a lot of existing code. Thoughts?
[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
category=core
severity=low
---
Site configuration information for perl 5.16.3:
Configured by Red Hat, Inc. at Mon Nov 11 12:49:48 UTC 2013.
Summary of my perl5 (revision 5 version 16 subversion 3) configuration:
Platform:
osname=linux, osvers=3.10.9-200.fc19.x86_64, archname=x86_64-linux-thread-multi
uname='linux buildvm-04.phx2.fedoraproject.org 3.10.9-200.fc19.x86_64 #1 smp wed aug 21 19:27:58 utc 2013 x86_64 x86_64 x86_64 gnulinux '
config_args='-des -Doptimize=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -Dccdlflags=-Wl,--enable-new-dtags -Dlddlflags=-shared -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -Wl,-z,relro -DDEBUGGING=-g -Dversion=5.16.3 -Dmyhostname=localhost -Dperladmin=root@localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dprefix=/usr -Dvendorprefix=/usr -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl5 -Dsitearch=/usr/local/lib64/perl5 -Dprivlib=/usr/share/perl5 -Dvendorlib=/usr/share/perl5/vendor_perl -Darchlib=/usr/lib64/perl5 -Dvendorarch=/usr/lib64/perl5/vendor_perl -Darchname=x86_64-linux-thread-multi -Dlibpth=/usr/local/lib64 /lib64 /usr/lib64 -Duseshrplib -Dusethreads -Duseithreads -Dusedtrace=/usr/bin/dtrace -Duselargefiles -Dd_semctl_semun -Di_db -Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio -Dinstallusrbinp
erl=n -Ubincompat5005 -Uversiononly -Dpager=/usr/bin/less -isr -Dd_gethostent_r_proto -Ud_endhostent_r_proto -Ud_sethostent_r_proto -Ud_endprotoent_r_proto -Ud_setprotoent_r_proto -Ud_endservent_r_proto -Ud_setservent_r_proto -Dscriptdir=/usr/bin -Dusesitecustomize'
hint=recommended, useposix=true, d_sigaction=define
useithreads=define, usemultiplicity=define
useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
use64bitint=define, use64bitall=define, uselongdouble=undef
usemymalloc=n, bincompat5005=undef
Compiler:
cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
optimize='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic',
cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
ccversion='', gccversion='4.7.2 20121109 (Red Hat 4.7.2-8)', gccosandvers=''
intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
alignbytes=8, prototype=define
Linker and Libraries:
ld='gcc', ldflags =' -fstack-protector'
libpth=/usr/local/lib64 /lib64 /usr/lib64
libs=-lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc -lgdbm_compat
perllibs=-lresolv -lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
libc=, so=so, useshrplib=true, libperl=libperl.so
gnulibc_version='2.16'
Dynamic Linking:
dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,--enable-new-dtags -Wl,-rpath,/usr/lib64/perl5/CORE'
cccdlflags='-fPIC', lddlflags='-shared -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -Wl,-z,relro '
Locally applied patches:
---
@INC for perl 5.16.3:
/home/eda/lib/perl5/
/usr/local/lib64/perl5
/usr/local/share/perl5
/usr/lib64/perl5/vendor_perl
/usr/share/perl5/vendor_perl
/usr/lib64/perl5
/usr/share/perl5
.
---
Environment for perl 5.16.3:
HOME=/home/tradingsystems
LANG=en_GB.UTF-8
LANGUAGE (unset)
LC_COLLATE=C
LC_CTYPE=en_GB.UTF-8
LC_MESSAGES=en_GB.UTF-8
LC_MONETARY=en_GB.UTF-8
LC_NUMERIC=en_GB.UTF-8
LC_TIME=en_GB.UTF-8
LD_LIBRARY_PATH (unset)
LOGDIR (unset)
PATH=/home/eda/bin:/home/eda/bin:/usr/local/bin:/usr/bin:/sbin:/usr/sbin:/sbin:/usr/sbin
PERL5LIB=/home/eda/lib/perl5/
PERL_BADLANG (unset)
SHELL=/bin/bash
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[perl #120863] foreach on hash keys should give readonly scalar
by Ed Avis