在MooseX :: Declare中创建BUILD方法的正确方法是什么？

Question

我BUILD在MooseX :: Declare中的方法有困难.如果我说:

#!/usr/bin/perl

use MooseX::Declare;

class Foo {
    has foo => (is => "rw", isa => "Str", default => "foo");

    method BUILD {
        print "I was called\n";
    }
}

Foo->new;

我得到以下不是有用的错误消息:

Reference found where even-sized list expected at /Users/cowens/perl5/lib/perl5/MooseX/Method/Signatures/Meta/Method.pm line 335.
Validation failed for 'MooseX::Types::Structured::Tuple[MooseX::Types::Structured::Tuple[Object],MooseX::Types::Structured::Dict[]]' failed with value [ [ Foo=HASH(0x804b20) ], { HASH(0x8049e0) => undef } ], Internal Validation Error is: Validation failed for 'MooseX::Types::Structured::Dict[]' failed with value { HASH(0x8049e0) => undef } at /Users/cowens/perl5/lib/perl5/MooseX/Method/Signatures/Meta/Method.pm line 365
        MooseX::Method::Signatures::Meta::Method::validate('MooseX::Method::Signatures::Meta::Method=HASH(0xb8aab0)', 'ARRAY(0xb8ab30)') called at /Users/cowens/perl5/lib/perl5/MooseX/Method/Signatures/Meta/Method.pm line 139
        Foo::BUILD('Foo=HASH(0x804b20)', 'HASH(0x8049e0)') called at generated method (unknown origin) line 25
        Foo::new('Foo') called at test.pl line 13

但如果我说:

#!/usr/bin/perl

use MooseX::Declare;

class Foo {
    has foo => (is => "rw", isa => "Str", default => "foo");

    sub BUILD {
        my $self = shift;
        print "I was called\n";
    }
}

Foo->new;

一切正常(但是丑陋且与其余代码不合适).

Answer 1

如果你不需要,BUILD会采取arg,只需说:

method BUILD($) { ... }

Answer 2

它失败了,因为BUILD需要一个arg方法签名.默认情况下,MooseX::Declare创建与BUILD调用方式不兼容的签名.(细节对我来说很模糊.)我知道因为我遇到过类似的错误一次.我当然同意错误信息可能更具启发性; 很多Moose的东西都是如此.

无论如何,我让它像这样工作:

use MooseX::Declare;

class Foo {
    has foo => (is => "rw", isa => "Str", default => "foo");

    method BUILD(Item $href) {
        print "I was called\n";
    }
}

Foo->new;

希望有所帮助.

您可以摆弄签名并尝试更具体的类型; 我认为Moose发送了一个尚未完成的对象的hashref作为参数.

Answer 3

Perl 能够理解sub，因此会在当前包的符号表中创建一个条目。&Foo::BUILD，在Devel::Declare和其他魔法之后从类闭包创建了一个包范围。

Moose专门寻找BUILDsub 来允许您操纵构造函数逻辑。我的猜测（尽管我没有完全追踪）是 MooseX 模块不妨碍 Moose 尝试做的事情。这样本地人BUILD就永远传递给 Moose magic 来确定构造函数逻辑。

另一方面，method关键字更具有Devel::Declare魔力，可以在元类结构中创建方法。