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[perl #113962] /r modifier on substitutions - variant returning undef if no match

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From:
Ed Avis
Date:
July 3, 2012 03:02
Subject:
[perl #113962] /r modifier on substitutions - variant returning undef if no match
Message ID:
rt-3.6.HEAD-28836-1341309716-902.113962-75-0@perl.org
# New Ticket Created by  "Ed Avis" 
# Please include the string:  [perl #113962]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org:443/rt3/Ticket/Display.html?id=113962 >


This is a bug report for perl from eda@waniasset.com,
generated with the help of perlbug 1.39 running under perl 5.14.2.


-----------------------------------------------------------------
[Please describe your issue here]

The new /r flag introduced for the s/// and tr/// operators in perl
5.14 is useful, but not as useful as it could be.  Careful programming
will often check that the substitution matched:

    my $old = 'cat';
    (my $new = $old) =~ s/cat/dog/ or die;

While the intention of /r is to simplify the use of substitution,
partly in idioms like the above and partly inside map {}, it is hard
to use it if you wanted to check that the substitution succeeded.
The code above cannot be straightforwardly rewritten using /r and
nor can you straightforwardly map {} over an array performing a
substitution on each item and checking it succeeded.

I suggest a variant which performs the substitution and returns
either the new string, or undef if no match.  Suppose the modifier
/R is used for this purpose.  Then

    my $new = $old =~ s/cat/dog/R // die;

    my @new = map { s/cat/dog/R // die } @old;

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=wishlist
---
This perlbug was built using Perl 5.14.2 in the Fedora build system.
It is being executed now by Perl 5.14.2 - Wed May 30 15:40:46 UTC 2012.

Site configuration information for perl 5.14.2:

Configured by Red Hat, Inc. at Wed May 30 15:40:46 UTC 2012.

Summary of my perl5 (revision 5 version 14 subversion 2) configuration:
   
  Platform:
    osname=linux, osvers=2.6.32-220.4.1.el6.x86_64,
archname=x86_64-linux-thread-multi
    uname='linux x86-17.phx2.fedoraproject.org 2.6.32-220.4.1.el6.x86_64
#1 smp thu jan 19 14:50:54 est 2012 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 -DDEBUGGING=-g -Dversion=5.14.2
-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
-Dinstallusrbinperl=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'
    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='4.6.3 20120306 (Red Hat 4.6.3-2)',
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='2.14.90'
  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'

Locally applied patches:
    

---
@INC for perl 5.14.2:
    /home/eda/lib/perl5//x86_64-linux-thread-multi
    /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 5.14.2:
    HOME=/home/eda
    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:/bin:/usr/bin:/sbin:/usr
/sbin:/sbin:/usr/sbin
    PERL5LIB=/home/eda/lib/perl5/
    PERL_BADLANG (unset)
    SHELL=/bin/bash



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