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;