Moose(Perl)：将undef转换为空字符串或0而不是die()

发布时间：2020-12-15 21:22:38 所属栏目：大数据来源：网络整理

导读：由于不完整的数据被提供给我的Moose构造函数,我收到了很多QA例外.属性名称存在于构造函数参数中,但值为undef. 对于许多脚本应用程序来说,这是事实上的事实.而且这通常很好.你不希望来自警告pragma的恼人的警告(所以你没有警告’未初始化’),你当然不希望你的

由于不完整的数据被提供给我的Moose构造函数,我收到了很多QA例外.属性名称存在于构造函数参数中,但值为undef.

对于许多脚本应用程序来说,这是事实上的事实.而且这通常很好.你不希望来自警告pragma的恼人的警告(所以你没有警告’未初始化’),你当然不希望你的代码死亡,因为一个小的值,比如housenumber,是undef.

所以不用多说,我希望我的Moose构造函数表现得像直接Perl(即没有使用警告’未初始化’),即将undef转换为0或根据需要将空字符串转换为空字符串.此示例中显示的尝试不适用于存在属性名称但值为undef的情况.我可以想到使用BUILDARGS实现我想要的.但是在没有resorting to MooseX::UndefTolerant的普通Moose中是否有一种声明性的方式(遗憾的是我不能使用,因为它没有安装)？

package AAA;
use Moose;
has 'hu',is => 'ro',isa => 'Str';
has 'ba',isa => 'Int';
no Moose; __PACKAGE__->meta->make_immutable;

package BBB;
use Moose; extends 'AAA';
has '+hu',default => ''; # don't want to die on undef
has '+ba',default => 0;  # idem
no Moose; __PACKAGE__->meta->make_immutable;

package main;
use Test::More;
use Test::Exception;
# Those AAAs should die ...
throws_ok { AAA->new( hu => undef ) }
    qr/Validation failed for 'Str' with value undef/;
throws_ok { AAA->new( ba => undef ) }
    qr/Validation failed for 'Int' with value undef/;
# .. but these BBBs should live:
lives_ok  { BBB->new( hu => undef ) } 'hu supplied as undef';
lives_ok  { BBB->new( ba => undef ) } 'ba supplied as undef';
done_testing;

解决方法

在 Moose::Manual::Types中有一种记录方式来处理这种问题.

使用Maybe [a]类型.

package AAA;
use Moose;

has 'hu',isa => 'Int';

no Moose; __PACKAGE__->meta->make_immutable;


package BBB;
use Moose; extends 'AAA';

has 'hu',is => 'rw',isa => 'Maybe[Str]',default => ''; # will not die on undef
has 'ba',isa => 'Maybe[Int]',default => 0;  # idem

sub BUILD {
    my $self = shift;
    $self->hu('') unless defined $self->hu;
    $self->ba(0) unless defined $self->ba;
}

no Moose; __PACKAGE__->meta->make_immutable;


package main;
use Test::More;
use Test::Exception;

# Those AAAs should die ...
throws_ok { AAA->new( hu => undef ) }
    qr/Validation failed for 'Str' with value undef/;
throws_ok { AAA->new( ba => undef ) }
    qr/Validation failed for 'Int' with value undef/;

# .. but these BBBs should live:
lives_ok  { BBB->new( hu => undef ) } 'hu supplied as undef';
lives_ok  { BBB->new( ba => undef ) } 'ba supplied as undef';

my $bbb = BBB->new( hu => undef,ba => undef );

is $bbb->hu,'',"hu is ''";
is $bbb->ba,'ba is 0';

done_testing;

（编辑：李大同）

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