[perl #68196] overload::import resets the setting of 'fallback'

# New Ticket Created by  Jeff Dairiki 
# Please include the string:  [perl #68196]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=68196 >



This is a bug report for perl from dairiki@dairiki.org,
generated with the help of perlbug 1.35 running under perl v5.8.8.


-----------------------------------------------------------------
Description: 
 
overload::import does not preserve any previously set fallback setting.

If one has more than one 'use overload' statements in the same package,
any fallback setting not in the final 'use overload' will be ignored.
E.g.

    use overload fallback => 1;
    use overload '""' => \&as_string;

is not equivalent to

    use overload fallback => 1, '""' => \&as_string;

as the second 'use overload' resets fallback to undef.



I'm using perl 5.8.8 from Debian etch, however from inspection of the current
git code at http://perl5.git.perl.org/perl.git/blame?f=lib/overload.pm
it appears this bug is still present in the latest versions of perl 5.



Test Script:

==== Begin overload_fallback.t ===
#!/usr/bin/perl -w
use warnings;
use strict;
use Test::More tests => 2;

use overload
    '""' => sub { 'stringvalue' },
    fallback => 1;

BEGIN {
    my $x = bless {}, 'main';
    ok $x eq 'stringvalue',  'fallback worked';
}


# NOTE: delete the next line and this test script will pass
use overload '+' => sub { die "unused"; };

my $x = bless {}, 'main';
ok $x eq 'stringvalue',  'fallback worked again';

==== End overload_fallback.t ===



Patch:

This patch is probably not optimal, but I think it works.

==== Begin overload.patch ====
--- /usr/share/perl/5.8.8/overload.pm   2008-12-18 07:26:08.000000000 -0800
+++ overload.pm 2009-08-04 17:45:52.000000000 -0700
@@ -10,6 +10,7 @@
   $package = shift;
   my %arg = @_;
   my ($sub, $fb);
+  $fb = ${$package . "::()"};
   $ {$package . "::OVERLOAD"}{dummy}++; # Register with magic by touching.
   *{$package . "::()"} = \&nil; # Make it findable via fetchmethod.
   for (keys %arg) {

==== End overload.patch ====

-----------------------------------------------------------------
---
Flags:
    category=library
    severity=low
---
Site configuration information for perl v5.8.8:

Configured by Debian Project at Fri Dec 19 00:43:54 EST 2008.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.18-6-686, archname=i486-linux-gnu-thread-multi
    uname='linux etch 2.6.18-6-686 #1 smp fri dec 12 16:48:28 utc 2008 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/lib/perl/5.8 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.8.8 -Dsitearch=/usr/local/lib/perl/5.8.8 -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 -Duseshrplib -Dlibperl=libperl.so.5.8.8 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef 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 -DTHREADS_HAVE_PIDS -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include'
    ccversion='', gccversion='4.1.2 20061115 (prerelease) (Debian 4.1.1-21)', 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
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.3.6.so, so=so, useshrplib=true, libperl=libperl.so.5.8.8
    gnulibc_version='2.3.6'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:
    

---
@INC for perl v5.8.8:
    /etc/perl
    /usr/local/lib/perl/5.8.8
    /usr/local/share/perl/5.8.8
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.8
    /usr/share/perl/5.8
    /usr/local/lib/site_perl
    .

---
Environment for perl v5.8.8:
    HOME=/home/dairiki
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=~/usr/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/bash

• [perl #68196] overload::import resets the setting of 'fallback' by Jeff Dairiki