获取 Data::Dumper 对象打印错误

Getting Data::Dumper Object print error

问题:

我正在尝试打印 $self 对象以了解包含的数据结构,如下行并收到错误:

use Data::Dumper;
my $self = shift;
print Dumper($self);

错误:

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

版本信息:

$ 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

我无法更新 perl 版本,我已尝试将 Data::Dumper 更新为 cpan install Data::Dumper;

安装后显示此 /usr/bin/make test -- OK

但当我再次检查时,版本仍然相同。

请问有什么办法可以解决这个问题吗?

或者我可以使用其他方式来打印所需的对象?

这重现了 Can't locate object method "FIRSTKEY" via package "Memoize::Expire" 错误(在 Perl 5.26 上测试):

use Memoize::Expire;
use Data::Dumper;
tie my %cache => 'Memoize::Expire';
print Dumper(\%cache);

我认为这可以被认为是 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 中的一个错误,尽管不幸的是该发行版似乎已经好几年没有维护了。 (你可能还想首先考虑你对 Memoize::Expire 的使用——你用它做什么,你真的需要它,等等)

由于 Data::Dumper 通常用于调试,我的问题是您是否真的需要查看 Memoize::Expire 对象的内容。如果是这样,您可以考虑切换到 Data::Dump because it provides Data::Dump::Filtered。虽然以下内容 不会 提供可以 eval 返回 Perl 的数据结构,但它有望为您提供有用的调试输出:

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;

输出:

# hashref tied to:
bless({
  C => { x => "Z\x8Cb[=12=][=12=][=12=][=12=]\xFF\xFFy" },
  LIFETIME => 0,
  NUM_USES => 0,
}, "Memoize::Expire")

最后,这是一个 IMO 丑陋的 hack 快速修复,其实现借用自 Tie::StdHash。这应该可以消除错误,但是 不会 向您显示对象的内部结构:

sub Memoize::Expire::FIRSTKEY { my $a = scalar keys %{$_[0]{C}}; each %{$_[0]{C}} }
sub Memoize::Expire::NEXTKEY  { each %{$_[0]{C}} }

$self 是一个绑定对象,其中一些绑定方法未实现。转储绑定对象的解决方法是转储基础对象

print Dumper(tied $self)

或者对象是否绑定不明确的情况下

print Dumper(tied $self || $self)