为什么在 BUILD 中修改 Moose 类会导致此错误？

Question

我在使用 BUILD 时遇到了与 Moose 相关的错误。当我更改为 BUILDALL 时，它似乎可以工作。请注意 Class::MOP::load_class 的使用

使用 BUILD

Perl version: 5.012002
Class::MOP::Version: 1.11
Moose::Version: 1.24
Applying fixup GV::WebServer::Fixups::Development
aflott-g3 at a.pl line 83.
Error: trying to call refresh() in GV::WebServer::Fixups::Development produced: The     'add_attribute' method cannot be called on an immutable instance at /opt/cidc-perl/perl-5.12.2/lib/perl5/x86_64-linux/Class/MOP/Class/Immutable/Trait.pm line 32
        Class::MOP::Class::Immutable::Trait::_immutable_cannot_call('add_attribute') called at /opt/cidc-perl/perl-5.12.2/lib/perl5/x86_64-linux/Class/MOP/Class/Immutable/Trait.pm line 37
        Class::MOP::Class:::around('CODE(0x13a2e028)', 'Class::MOP::Class::Immutable::Moose::Meta::Class=HASH(0x13d58...', 'architecture', 'is', 'ro', 'isa', 'Str', 'lazy', 1, ...) called at /opt/cidc-perl/perl-5.12.2/lib/perl5/x86_64-linux/Class/MOP/Method/Wrapped.pm line 159
        Class::MOP::Method::Wrapped::__ANON__('Class::MOP::Class::Immutable::Moose::Meta::Class=HASH(0x13d58...', 'architecture', 'is', 'ro', 'isa', 'Str', 'lazy', 1, 'default', ...) called at /opt/cidc-perl/perl-5.12.2/lib/perl5/x86_64-linux/Class/MOP/Method/Wrapped.pm line 89
        Class::MOP::Class::Immutable::Moose::Meta::Class::add_attribute('Class::MOP::Class::Immutable::Moose::Meta::Class=HASH(0x13d58...', 'architecture', 'is', 'ro', 'isa', 'Str', 'lazy', 1, 'default', ...) called at a.pl line 47
        Amethyst::SystemInfo::BUILD('Amethyst::SystemInfo=HASH(0x13e83010)', 'HASH(0x13e50cc0)') called at generated method (unknown origin) line 147
        Amethyst::SystemInfo::new('Amethyst::SystemInfo') called at a.pl line 92
        GV::WebServer::Fixups::AutoSet::set() called at a.pl line 84
        GV::WebServer::Fixups::Development::refresh('GV::WebServer::Fixups::Development') called at a.pl line 114
        main::__ANON__() called at /opt/cidc-perl/perl-5.12.2/lib/perl5/Try/Tiny.pm line 76
        eval {...} called at /opt/cidc-perl/perl-5.12.2/lib/perl5/Try/Tiny.pm line 67
        Try::Tiny::try('CODE(0x13e82fe0)', 'Try::Tiny::Catch=REF(0x13e8cd50)') called at a.pl line 118

使用 BUILDALL：

Perl version: 5.012002
Class::MOP::Version: 1.11
Moose::Version: 1.24
Applying fixup GV::WebServer::Fixups::Development
aflott-g3 at a.pl line 71.
aflott-g3364136 at a.pl line 81.

完整错误

从此代码中：

package Amethyst::SystemInfo;

use v5.10;

use Moose;

use Sys::Hostname qw();
use Sys::HostIP;
use Try::Tiny;

has '_host_ip' => ('is' => 'ro', 'isa' => 'Sys::HostIP', 'default' => sub { Sys::HostIP->new });
has 'eth0_ipv4' => ('is' => 'rw', 'isa' => 'Str',);
has 'ethernet_interfaces' => ('is' => 'rw', 'isa' => 'HashRef',);
has 'hostname' => ('is' => 'ro', 'isa' => 'Str', 'default' => sub { Sys::Hostname::hostname });

sub BUILD {
    my ($self) = @_;

    $self->ethernet_interfaces($self->_host_ip->interfaces);

    if ($self->ethernet_interfaces->{'eth0'}) {
        $self->eth0_ipv4($self->ethernet_interfaces->{'eth0'});
    }

    foreach my $attrib (
        qw(architecture domain fqdn kernel kernelrelease kernelversion memorytotal operatingsystem processor processorcount swap)
      ) {
        $self->meta->add_attribute(
            $attrib => (
                'is'      => 'ro',
                'isa'     => 'Str',
                'lazy'    => 1,
                'default' => sub { return $self->_load_value($attrib) }
            )
        );
    }

    $self->meta->make_immutable;

    return;
}

sub _load_value {
    my ($self, $module_name) = @_;

    try {
        Class::MOP::load_class("Pfacter::$module_name");
    }
    catch {
        warn("Failed to load Pfacter::$module_name");
    };

    my $value = "Pfacter::$module_name"->pfact({'pfact' => {'kernel' => 'Linux'}});

    unless (defined($value)) {
        warn("finding value for $module_name returned undef");
    }

    chomp($value);

    return $value;
}

no Moose;

package GV::WebServer::Fixups::Development;

use v5.10;

sub refresh {
    warn Amethyst::SystemInfo->new->hostname;
    return GV::WebServer::Fixups::AutoSet::set();
}

package GV::WebServer::Fixups::AutoSet;

use v5.10;

sub set {
    my $sysinfo = Amethyst::SystemInfo->new;
    warn $sysinfo->hostname, ' ', $sysinfo->swap;
}

package main;

use v5.10;

use Class::MOP;
use Try::Tiny;

my $module_name = "GV::WebServer::Fixups::Development";

say('Perl version: ',        $]);
say('Class::MOP::Version: ', $Class::MOP::VERSION);
say('Moose::Version: ',      $Moose::VERSION);
say("Applying fixup $module_name");

Class::MOP::load_class($module_name);

my $ret;
try {
    $ret = $module_name->refresh;
}
catch {
    warn("Error: trying to call refresh() in $module_name produced: " . shift);
};

Answer 1

每次构造该类的对象时，您都会修改该类。这没有任何意义。只需将类构造代码从 BUILD 和 BUILDARGS 中移出，并将其与其余的类构造代码放在一起即可。

package Amethyst::SystemInfo;

use v5.10;

use Moose;

use Sys::Hostname qw();
use Sys::HostIP;
use Try::Tiny;

has '_host_ip' => ('is' => 'ro', 'isa' => 'Sys::HostIP', 'default' => sub { Sys::HostIP->new });
has 'eth0_ipv4' => ('is' => 'rw', 'isa' => 'Str',);
has 'ethernet_interfaces' => ('is' => 'rw', 'isa' => 'HashRef',);
has 'hostname' => ('is' => 'ro', 'isa' => 'Str', 'default' => sub { Sys::Hostname::hostname });

foreach my $attrib (qw(
    architecture domain fqdn kernel kernelrelease kernelversion
    memorytotal operatingsystem processor processorcount swap
)) {
    has $attrib => (
        'is'      => 'ro',
        'isa'     => 'Str',
        'lazy'    => 1,
        'default' => sub { return $_[0]->_load_value($attrib) },
    );
}

sub BUILD {
    my ($self) = @_;

    $self->ethernet_interfaces($self->_host_ip->interfaces);

    if ($self->ethernet_interfaces->{'eth0'}) {
        $self->eth0_ipv4($self->ethernet_interfaces->{'eth0'});
    }
}

sub _load_value {
    ...
}

no Moose;
__PACKAGE__->meta->make_immutable;

1;

感谢 phaylon 和 bvr。