重写对象属性-使用Moose的最佳方法?
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让我们看看显然仅基于问题标题发布的SO问题输入机器人的预测是否将实现:
您要提出的问题似乎很主观,很可能已经解决。
使用Perl / Moose,我想弥合两种表示商人文章的方式之间的不匹配。令文章具有
name
,quantity
和price
。表示此问题的第一种方法是将数量设置为任何数字值,包括十进制值,因此您可以使用3.5米的绳索或电缆。我必须与之交互的第二个元素是a,不灵活,并且要求ѭ1是整数。因此,我必须重写对象以将quantity
设置为1,并将实际数量包括在name
中。 (是的,这是一个hack,但我想使示例保持简单。)
因此,这里的故事是一个属性的值会影响其他属性的值。
这是工作代码:
#!perl
package Article;
use Moose;
has name => is => \'rw\', isa => \'Str\', required => 1;
has quantity => is => \'rw\', isa => \'Num\', required => 1;
has price => is => \'rw\', isa => \'Num\', required => 1;
around BUILDARGS => sub {
my $orig = shift;
my $class = shift;
my %args = @_ == 1 ? %{$_[0]} : @_;
my $q = $args{quantity};
if ( $q != int $q ) {
$args{name} .= \" ($q)\";
$args{price} *= $q;
$args{quantity} = 1;
}
return $class->$orig( %args );
};
sub itemprice { $_[0]->quantity * $_[0]->price }
sub as_string {
return sprintf \'%2u * %-40s (%7.2f) %8.2f\', map $_[0]->$_,
qw/quantity name price itemprice/;
}
package main;
use Test::More;
my $table = Article->new({ name => \'Table\', quantity => 1, price => 199 });
is $table->itemprice, 199, $table->as_string;
my $chairs = Article->new( name => \'Chair\', quantity => 4, price => 45.50 );
is $chairs->itemprice, 182, $chairs->as_string;
my $rope = Article->new( name => \'Rope\', quantity => 3.5, price => 2.80 );
is $rope->itemprice, 9.80, $rope->as_string;
is $rope->quantity, 1, \'quantity set to 1\';
is $rope->name, \'Rope (3.5)\', \'name includes original quantity\';
done_testing;
但是,我想知道在Moose中是否有更好的成语来做到这一点。但是也许我的问题是主观的,应该迅速结束。 :-)
根据perigrin的答案进行更新
我已经改编了perigrin的代码示例(较小的错误和5.10语法),并将测试标记在其结尾:
package Article::Interface;
use Moose::Role;
requires qw(name quantity price);
sub itemprice { $_[0]->quantity * $_[0]->price }
sub as_string {
return sprintf \'%2u * %-40s (%7.2f) %8.2f\', map $_[0]->$_,
qw/quantity name price itemprice/;
}
package Article::Types;
use Moose::Util::TypeConstraints;
class_type \'Article::Internal\';
class_type \'Article::External\';
coerce \'Article::External\' =>
from \'Article::Internal\' => via
{
Article::External->new(
name => sprintf( \'%s (%s)\', $_->name, $_->quantity ),
quantity => 1,
price => $_->quantity * $_->price
);
};
package Article::Internal;
use Moose;
use Moose::Util::TypeConstraints;
has name => isa => \'Str\', is => \'rw\', required => 1;
has quantity => isa => \'Num\', is => \'rw\', required => 1;
has price => isa => \'Num\', is => \'rw\', required => 1;
my $constraint = find_type_constraint(\'Article::External\');
=useless for this case
# Moose::Manual::Construction - \"You should never call $self->SUPER::BUILD,
# nor\"should you ever apply a method modifier to BUILD.\"
sub BUILD {
my $self = shift;
my $q = $self->quantity;
# BUILD does not return the object to the caller,
# so it CANNOT BE USED to trigger the coercion.
return $q == int $q ? $self : $constraint->coerce( $self );
}
=cut
with qw(Article::Interface); # need to put this at the end
package Article::External;
use Moose;
has name => isa => \'Str\', is => \'ro\', required => 1;
has quantity => isa => \'Int\', is => \'ro\', required => 1;
has price => isa => \'Num\', is => \'ro\', required => 1;
sub itemprice { $_[0]->price } # override
with qw(Article::Interface); # need to put this at the end
package main;
use Test::More;
my $table = Article::Internal->new(
{ name => \'Table\', quantity => 1, price => 199 });
is $table->itemprice, 199, $table->as_string;
is $table->quantity, 1;
is $table->name, \'Table\';
my $chairs = Article::Internal->new(
name => \'Chair\', quantity => 4, price => 45.50 );
is $chairs->itemprice, 182, $chairs->as_string;
is $chairs->quantity, 4;
is $chairs->name, \'Chair\';
my $rope = Article::Internal->new(
name => \'Rope\', quantity => 3.5, price => 2.80 );
# I can trigger the conversion manually.
$rope = $constraint->coerce( $rope );
# I\'d like the conversion to be automatic, though.
# But I cannot use BUILD for doing that. - XXX
# Looks like I\'d have to add a factory method that inspects the
# parameters and does the conversion if needed, and it is always
# needed when the `quantity` isn\'t an integer.
isa_ok $rope, \'Article::External\';
is $rope->itemprice, 9.80, $rope->as_string;
is $rope->quantity, 1, \'quantity set to 1\';
is $rope->name, \'Rope (3.5)\', \'name includes original quantity\';
done_testing;
我同意这可以更好地分离关注点。另一方面,我不认为这对我来说是一个更好的解决方案,因为它增加了复杂性,并且没有提供自动转换(为此我必须添加更多的代码)。
没有找到相关结果
已邀请:
1 个回复
夏瓤跋棘
然后,您有一个Class来代表您的内部Articles,同样,这很简单。
最后,您有一堂课来代表您的外部文章。在这一步中,您必须重写接口中的某些方法,以处理您的属性将被专门化的事实[^ 1]。
最后,您定义一个简单的强制例程在两者之间进行转换。
您可以使用以下方法手动触发此强制:
另外,MooseX :: Types可以用于最后一部分以提供更清洁的糖,但是我选择在这里坚持使用纯Moose。 [^ 1]:您可能已经注意到,我已将“外部”文章中的属性设为只读。从您所说的来看,这些对象应该是“仅使用”,但是如果您需要可写的属性,则需要在数量上定义一个强制变量,以确保仅存储整数。我会将其作为练习留给读者。