通过 introduction to Object Oriented Perl with Moose，你应该大致的熟悉了Moose的类型检查系统。

设定类型为Int

第一个例子:

use strict;
use warnings;
use v5.10;

use Person;

my $student = Person->new( name => 'Joe' );
$student->year(1988);
say $student->year;
$student->year('23 years ago');

加载Person模块(类), 我们通过调用类的构造器"new"来创建对象$student。之后调用访问器"year", 设值为1998。在打印完后尝试将它设为"23 years ago"。

在模块中我们能看到有两个属性。 "year"属性有一个值是Int的isa项。因此, Moose的设置器把它的值限定为整型。

package Person;
use Moose;

has 'name' => (is => 'rw');
has 'year' => (isa => 'Int', is => 'rw');

1;

将模块保存在"somedir/lib/Person.pm"，脚本保存在"somedir/bin/app.pl" 然后在somedir文件夹下通过"perl -Ilib bin/app.pl"执行脚本

打印完值1988之后, 我们得到如下错误提示:

Attribute (year) does not pass the type constraint because:
   Validation failed for 'Int' with value "23 years ago"
       at accessor Person::year (defined at lib/Person.pm line 5) line 4
   Person::year('Person=HASH(0x19a4120)', '23 years ago')
       called at script/person.pl line 13

错误信息显示:Moose不能接受"23 years ago"作为一个整数。

用其它类作为类型限制

除了 默认类型限制, Moose也允许你使用任何已有的类名作为类型限定。

例如我们声明"birthday"属性是一个DateTime对象。

package Person;
use Moose;

has 'name'     => (is => 'rw');
has 'birthday' => (isa => 'DateTime', is => 'rw');

1;

脚本:

use strict;
use warnings;
use v5.10;

use Person;
use DateTime;

my $student = Person->new( name => 'Joe' );
$student->birthday( DateTime->new( year => 1988, month => 4, day => 17) );
say $student->birthday;
$student->birthday(1988);

可以看到, 第一次对"birthday"设置器的调用, 以DateTime对象作为参数。这样的调用没有问题。第二次调用使用了数字参数1998, 则抛出了和之前类似的异常:

Attribute (birthday) does not pass the type constraint because:
    Validation failed for 'DateTime' with value 1988
       at accessor Person::birthday (defined at lib/Person.pm line 5) line 4
    Person::birthday('Person=HASH(0x2143928)', 1988)
       called at script/person.pl line 14