Getting Data::Dumper Object print error - perl

Question

Problem:
I am trying to print the $self object to know the contained data structure like below line and getting the error:
use Data::Dumper;
my $self = shift;
print Dumper($self);
Error:
Can't locate object method "FIRSTKEY" via package "Memoize::Expire" at /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi/Data/Dumper.pm line 158
Version Information:
$ perl -MData::Dumper -le 'print Data::Dumper->VERSION';
2.121
$ perl -MMemoize::Expire -le 'print Memoize::Expire->VERSION';
1.03
$ perl -V
Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
Platform:
osname=linux, osvers=2.6.18-53.1.14.el5pae, archname=i386-linux-thread-multi
uname='linux builder16.centos.org 2.6.18-53.1.14.el5pae #1 smp wed mar 5 12:07:47 est 2008 i686 athlon i386 gnulinux '
config_args='-des -Doptimize=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -Dversion=5.8.8 -Dmyhostname=localhost -Dperladmin=root#localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dinstallprefix=/usr -Dprefix=/usr -Darchname=i386-linux -Dvendorprefix=/usr -Dsiteprefix=/usr -Duseshrplib -Dusethreads -Duseithreads -Duselargefiles -Dd_dosuid -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 -Dinc_version_list=5.8.7 5.8.6 5.8.5 -Dscriptdir=/usr/bin'
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='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -I/usr/include/gdbm',
optimize='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables',
cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -I/usr/include/gdbm'
ccversion='', gccversion='4.1.2 20071124 (Red Hat 4.1.2-42)', 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='gcc', ldflags =' -L/usr/local/lib'
libpth=/usr/local/lib /lib /usr/lib
libs=-lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc
perllibs=-lresolv -lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
libc=/lib/libc-2.5.so, so=so, useshrplib=true, libperl=libperl.so
gnulibc_version='2.5'
Dynamic Linking:
dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib/perl5/5.8.8/i386-linux-thread-multi/CORE'
cccdlflags='-fPIC', lddlflags='-shared -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -L/usr/local/lib'
Characteristics of this binary (from libperl):
Compile-time options: MULTIPLICITY PERL_IMPLICIT_CONTEXT
PERL_MALLOC_WRAP USE_ITHREADS USE_LARGE_FILES
USE_PERLIO USE_REENTRANT_API
Built under linux
Compiled at Sep 17 2008 13:37:09
#INC:
/usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.7/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.6/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.5/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.8
/usr/lib/perl5/site_perl/5.8.7
/usr/lib/perl5/site_perl/5.8.6
/usr/lib/perl5/site_perl/5.8.5
/usr/lib/perl5/site_perl
/usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.7/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.6/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.5/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.8
/usr/lib/perl5/vendor_perl/5.8.7
/usr/lib/perl5/vendor_perl/5.8.6
/usr/lib/perl5/vendor_perl/5.8.5
/usr/lib/perl5/vendor_perl
/usr/lib/perl5/5.8.8/i386-linux-thread-multi
/usr/lib/perl5/5.8.8
I can not update perl version, I have tried updating Data::Dumper with cpan install Data::Dumper;.
Which shows this /usr/bin/make test -- OK after installation.
But when I check again the version remains the same.
So Is there any way I can solve this problem?
Or I could use some other way to print the desired Object?

Answer 1

This reproduces the Can't locate object method "FIRSTKEY" via package "Memoize::Expire" error (tested on Perl 5.26):
use Memoize::Expire;
use Data::Dumper;
tie my %cache => 'Memoize::Expire';
print Dumper(\%cache);
I think this could be considered a bug in Memoize::Expire: it doesn't provide the FIRSTKEY and NEXTKEY implementations that Data::Dumper needs. You may want to report a bug in the issue tracker, although unfortunately the distribution seems unmaintained for several years. (You might also want to consider your use of Memoize::Expire in the first place - what are you using it for, do you really need it, etc.)
Since Data::Dumper is typically used for debugging, my question would be if you really need to see the contents of the Memoize::Expire object. If so, you might consider switching to Data::Dump because it provides Data::Dump::Filtered. While the following will not provide a data structure that can be evaled back to Perl, it will hopefully give you useful debug output:
use warnings;
use strict;
use Memoize::Expire;
use Data::Dump;
use Data::Dump::Filtered 'add_dump_filter';
add_dump_filter sub {
my ($ctx, $ref) = #_;
if ($ctx->reftype eq 'HASH' && defined(tied(%$ref))) {
return { comment=>"hashref tied to:",
object=>tied(%$ref) };
}
return undef; # normal processing
};
tie my %cache => 'Memoize::Expire';
$cache{x}='y';
dd \%cache;
Output:
# hashref tied to:
bless({
C => { x => "Z\x8C\25b\0\0\0\0\xFF\xFFy" },
LIFETIME => 0,
NUM_USES => 0,
}, "Memoize::Expire")
Finally, here's an IMO ugly hack quick fix with implementations borrowed from Tie::StdHash. This should get rid of the error but will however not show you the internal structure of the object:
sub Memoize::Expire::FIRSTKEY { my $a = scalar keys %{$_[0]{C}}; each %{$_[0]{C}} }
sub Memoize::Expire::NEXTKEY { each %{$_[0]{C}} }

Answer 2

$self is a tie'd object with some of the tied methods unimplemented. A workaround to dumping the tied object is to dump the underlying object
print Dumper(tied $self)
or in cases where it is ambiguous whether the object is tied or not
print Dumper(tied $self || $self)