在Moose中创建类属性的最佳方式是什么？

问题描述：

#!/usr/bin/perl 

use 5.010; 
use strict; 
use warnings; 
use MooseX::Declare; 

class User { 
    has id  => (isa => "Str", is => 'ro', builder => '_get_id'); 
    has name => (isa => "Str", is => 'ro'); 
    has balance => (isa => "Num", is => 'rw', default => 0); 

    #FIXME: this should use a database 
    method _get_id { 
     state $id = 0; #I would like this to be a class attribute 
     return $id++; 
    } 
} 

my @users; 
for my $name (qw/alice bob charlie/) { 
    push @users, User->new(name => $name); 
}; 

for my $user (@users) { 
    print $user->name, " has an id of ", $user->id, "\n"; 
}

答

我发现MooseX :: ClassAttribute，但它看起来很丑。这是最干净的方式吗？

#!/usr/bin/perl 

use 5.010; 
use strict; 
use warnings; 
use MooseX::Declare; 

class User { 
    use MooseX::ClassAttribute; 

    class_has id_pool => (isa => "Int", is => 'rw', default => 0); 

    has id  => (isa => "Str", is => 'ro', builder => '_get_id'); 
    has name => (isa => "Str", is => 'ro'); 
    has balance => (isa => "Num", is => 'rw', default => 0); 

    #FIXME: this should use a database 
    method _get_id { 
     return __PACKAGE__->id_pool(__PACKAGE__->id_pool+1); 
    } 
} 

my @users; 
for my $name (qw/alice bob charlie/) { 
    push @users, User->new(name => $name); 
}; 

for my $user (@users) { 
    print $user->name, " has an id of ", $user->id, "\n"; 
}

这是正确的方法。你也可以创建一个类类（如果你喜欢它们在一个单独的包中），看看ClassAttribute在底层做什么 – castaway 2009-07-08 07:09:47

不是`use strict`和`use warnings`冗余于`use MooseX :: Declare` ？ – 2009-12-09 23:41:36

答

老实说，我不认为这是所有麻烦的类属性的必要。对于只读类的属性，我只是使用一个返回常量的子。对于读写属性，在包一个简单的状态变量，通常的伎俩（我还没有碰到地方，我需要一些更复杂的任何方案。）

state $count = 0; 
method _get_id { 
    return ++$count; 
}

用词汇专用块可如果您需要5.10之前的兼容性，请使用此选项

在Moose中创建类属性的最佳方式是什么？

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