perl - 驼鹿 (Perl) : convert undef to empty string or 0 rather than die()

Question

我已收到 很多异常(exception)由于向我的 Moose 构造函数提供了不完整的数据，因此来自 QA。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，事实就是如此undef .通常，这完全没问题。您不希望来自 warnings 的烦人警告pragma (所以你做 no warnings 'uninitialized' )，你当然不希望你的代码死，因为一个小值，比如门牌号码，是 undef .

所以不用多说，我希望我的 Moose 构造函数表现得像直接的 Perl(即没有 use warnings 'uninitialized')，也就是转换 undef至 0或根据需要使用空字符串。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。 .我可以考虑使用 BUILDARGS实现我想要的。但是在没有 resorting to MooseX::UndefTolerant 的普通 Moose 中是否有一种声明方式？ (不幸的是我不能使用它，因为它没有安装)？

package AAA;
use Moose;
has 'hu', is => 'ro', isa => 'Str';
has 'ba', is => 'ro', 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;

Answer 1

在 Moose::Manual::Types是一种有记录的方法来处理这种问题。

使用 Maybe[a]类型。

package AAA;
use Moose;

has 'hu', is => 'ro', isa => 'Str';
has 'ba', is => 'ro', 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', is => 'rw', 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, 0, 'ba is 0';

done_testing;