我试图在旧的和大型的Perl项目中记录数据结构。为了做到这一点，我使用Data::Dumper，但是，有些结构有点太大并且垃圾邮件日志。所以我正在寻找一种以不那么冗长的方式记录它们的方法。
现在，Dumper的doc提到$Data::Dumper::Freezer = <method_name>变量，可以用来解决这个问题。我尝试过使用它。
添加一个返回＆＃34;缩短＆＃34;的序列化方法。虽然该方法被调用，但值不会产生任何结果。使序列化方法对$ _ [0]起作用会产生所需的效果，但会破坏原始数据结构。
我很困惑。我究竟做错了什么？我该如何解决？
这是一个精致的示例代码：
#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;
$Data::Dumper::Indent = 0;
$\="\n";
my $x = Foo->new ( answer => 42, use => "force" );
my $y = { foo => $x };
print "initial plain:\n\t", Dumper( $x );
print "initial compound:\n\t", Dumper( $y );
{
local $Data::Dumper::Freezer = 'freeze_pure';
print "still not abbreviated data:\n\t", Dumper( $y );
};
{
local $Data::Dumper::Freezer = 'freeze_replace';
print "abbreviated data:\n\t", Dumper( $y );
};
print "initial data is still intact:\n\t", Dumper( $x );
print "compound data is corrupted:\n\t", Dumper( $y );
package Foo;
sub new {
my $class = shift;
return bless { @_ }, $class;
};
sub freeze_pure {
my $self = $_[0];
warn "# In freeze_pure";
return bless {
values => join ",", values %$self
}, (ref $self) . "::short";
};
sub freeze_replace {
my $self = $_[0];
warn "# In freeze_replace";
$_[0] = bless {
values => join ",", values %$self
}, (ref $self) . "::short";
return;
};
输出：
initial plain:
$VAR1 = bless( {'use' => 'force','answer' => 42}, 'Foo' );
initial compound:
$VAR1 = {'foo' => bless( {'use' => 'force','answer' => 42}, 'Foo' )};
# In freeze_pure at dumper-freezer.pl line 36.
still not abbreviated data:
$VAR1 = {'foo' => bless( {'use' => 'force','answer' => 42}, 'Foo' )};
# In freeze_replace at dumper-freezer.pl line 42.
abbreviated data:
$VAR1 = {'foo' => bless( {'values' => 'force,42'}, 'Foo::short' )};
initial data is still intact:
$VAR1 = bless( {'use' => 'force','answer' => 42}, 'Foo' );
compound data is corrupted:
$VAR1 = {'foo' => bless( {'values' => 'force,42'}, 'Foo::short' )};
答案 0 :(得分：4)
虽然文档有点稀疏，但冷冻/烤面包机的预期用途是数据序列化/反序列化，而不是调试输出的预处理。
因此，Data :: Dumper调用freezer方法，但不使用返回值。这个想法可能是因为如果你要对一个对象进行序列化，那么在你对它进行反序列化之前，你不会再次搞乱它，所以更改对象本身没有问题。
以下是Data :: Dumper源中的relevant section of code：
# Call the freezer method if it's specified and the object has the
# method. Trap errors and warn() instead of die()ing, like the XS
# implementation.
my $freezer = $s->{freezer};
if ($freezer and UNIVERSAL::can($val, $freezer)) {
eval { $val->$freezer() };
warn "WARNING(Freezer method call failed): $@" if $@;
}
如果您只想减少日志中输出的大小，可以通过将$Data::Dumper::Indent设置为零来删除换行符和缩进：
use Data::Dumper;
use WWW::Mechanize;
$Data::Dumper::Indent = 0;
my $mech = WWW::Mechanize->new;
print Dumper $mech;
输出：
$VAR1 = bless( {'headers' => {},'ssl_opts' => {'verify_hostname' => 1},'forms' => undef,'page_stack' => [],'text' => undef,'requests_redirectable' => ['GET','HEAD','POST'],'timeout' => 180,'onerror' => sub { "DUMMY" },'current_form' => undef,'links' => undef,'max_redirect' => 7,'quiet' => 0,'images' => undef,'noproxy' => 0,'stack_depth' => 8675309,'show_progress' => undef,'protocols_forbidden' => undef,'no_proxy' => [],'handlers' => {'request_prepare' => bless( [{'owner' => 'LWP::UserAgent::cookie_jar','callback' => sub { "DUMMY" },'line' => '/home/foo/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/LWP/UserAgent.pm:705'}], 'HTTP::Config' ),'response_header' => bless( [{'owner' => 'LWP::UserAgent::parse_head','callback' => sub { "DUMMY" },'m_media_type' => 'html','line' => '/home/foo/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/LWP/UserAgent.pm:684'}], 'HTTP::Config' ),'response_done' => bless( [{'owner' => 'LWP::UserAgent::cookie_jar','callback' => sub { "DUMMY" },'line' => '/home/foo/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/LWP/UserAgent.pm:708'}], 'HTTP::Config' )},'onwarn' => sub { "DUMMY" },'protocols_allowed' => undef,'use_eval' => 1,'local_address' => undef,'autocheck' => 1,'title' => undef,'def_headers' => bless( {'user-agent' => 'WWW-Mechanize/1.75'}, 'HTTP::Headers' ),'cookie_jar' => bless( {'COOKIES' => {}}, 'HTTP::Cookies' ),'proxy' => {},'max_size' => undef}, 'WWW::Mechanize' );
这仍然是很多输出，但它肯定比以下更紧凑：
$VAR1 = bless( {
'headers' => {},
'ssl_opts' => {
'verify_hostname' => 1
},
'forms' => undef,
'page_stack' => [],
'text' => undef,
'requests_redirectable' => [
'GET',
'HEAD',
'POST'
],
'timeout' => 180,
'onerror' => sub { "DUMMY" },
'current_form' => undef,
'links' => undef,
'max_redirect' => 7,
'quiet' => 0,
'images' => undef,
'noproxy' => 0,
'stack_depth' => 8675309,
'show_progress' => undef,
'protocols_forbidden' => undef,
'no_proxy' => [],
'handlers' => {
'request_prepare' => bless( [
{
'owner' => 'LWP::UserAgent::cookie_jar',
'callback' => sub { "DUMMY" },
'line' => '/home/foo/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/LWP/UserAgent.pm:705'
}
], 'HTTP::Config' ),
'response_header' => bless( [
{
'owner' => 'LWP::UserAgent::parse_head',
'callback' => sub { "DUMMY" },
'm_media_type' => 'html',
'line' => '/home/foo/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/LWP/UserAgent.pm:684'
}
], 'HTTP::Config' ),
'response_done' => bless( [
{
'owner' => 'LWP::UserAgent::cookie_jar',
'callback' => sub { "DUMMY" },
'line' => '/home/foo/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/LWP/UserAgent.pm:708'
}
], 'HTTP::Config' )
},
'onwarn' => sub { "DUMMY" },
'protocols_allowed' => undef,
'use_eval' => 1,
'local_address' => undef,
'autocheck' => 1,
'title' => undef,
'def_headers' => bless( {
'user-agent' => 'WWW-Mechanize/1.75'
}, 'HTTP::Headers' ),
'cookie_jar' => bless( {
'COOKIES' => {}
}, 'HTTP::Cookies' ),
'proxy' => {},
'max_size' => undef
}, 'WWW::Mechanize' );
或者，您可以尝试Data::Dump，这样您就可以使用Data::Dump::Filtered过滤输出。我更喜欢Data :: Dump到Data :: Dumper，因为我认为它有更明智的默认值（例如输出空格以外的空格的转义序列）。
我还没有使用过滤功能，但是brian d foy用几个例子写了a nice article。