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[perl #69384] numericness failure in sorting

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From:
Zefram
Date:
September 25, 2009 07:04
Subject:
[perl #69384] numericness failure in sorting
Message ID:
rt-3.6.HEAD-21832-1253881290-1868.69384-75-0@perl.org
# New Ticket Created by  Zefram 
# Please include the string:  [perl #69384]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=69384 >



This is a bug report for perl from zefram@fysh.org,
generated with the help of perlbug 1.36 running under perl 5.10.0.


-----------------------------------------------------------------
[Please enter your report here]

$ perl -lwe 'sub my_cmp { $_[0] < $_[1] ? "-1" : $_[0] == $_[1] ? "0" : "1" } print sort { my_cmp($a, $b) } (1,5,4,7,2)'
Sort subroutine didn't return a numeric value at -e line 1.

Strings such as "-1" are meant to be adequately numeric for Perl purposes,
but sort is being picky.  Can work around this by changing the comparator
block thus:

$ perl -lwe 'sub my_cmp { $_[0] < $_[1] ? "-1" : $_[0] == $_[1] ? "0" : "1" } print sort { 0 + my_cmp($a, $b) } (1,5,4,7,2)'
12457

Can also work around it by side-effect numerification:

$ perl -lwe 'sub my_cmp { my $r = $_[0] < $_[1] ? "-1" : $_[0] == $_[1] ? "0" : "1"; { no warnings "void"; 0+$r; } return $r; } print sort { my_cmp($a, $b) } (1,5,4,7,2)'
12457

In the real application behind this bug report, there is actually
good reason for the cmp function to generate its results as strings.
I'll probably do side-effect numerification as a permanent workaround for
the cmp function.  Of course, sort will still screw up when presented with
string-based numbers generated by anything that's not built specifically
to work with sort.

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=low
---
Site configuration information for perl 5.10.0:

Configured by Debian Project at Fri Aug 28 22:30:10 UTC 2009.

Summary of my perl5 (revision 5 version 10 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.6.26-2-amd64, archname=i486-linux-gnu-thread-multi
    uname='linux puccini 2.6.26-2-amd64 #1 smp fri aug 14 07:12:04 utc 2009 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.10 -Darchlib=/usr/lib/perl/5.10 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.10.0 -Dsitearch=/usr/local/lib/perl/5.10.0 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.10.0 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=undef, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2 -g',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include'
    ccversion='', gccversion='4.3.2', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib /usr/lib64
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.7.so, so=so, useshrplib=true, libperl=libperl.so.5.10.0
    gnulibc_version='2.7'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib'

Locally applied patches:
    

---
@INC for perl 5.10.0:
    /etc/perl
    /usr/local/lib/perl/5.10.0
    /usr/local/share/perl/5.10.0
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.10
    /usr/share/perl/5.10
    /usr/local/lib/site_perl
    .

---
Environment for perl 5.10.0:
    HOME=/home/zefram
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/zefram/pub/i686-pc-linux-gnu/bin:/home/zefram/pub/common/bin:/usr/bin:/usr/X11R6/bin:/bin:/usr/local/bin:/usr/games
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh


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