perl - 如何在 Moose 中定义默认属性属性值？

Question

正如标题所暗示的，我希望能够在我的类里面做这样的事情:

use MooseX::Declare;

class MyClass {
    default_attribute_propeties(
        is       => 'ro',
        lazy     => 1,
        required => 1,
    );

    has [qw( some standard props )] => ();

    has 'override_default_props' => (
        is       => 'rw',
        required => 0,
        ...
    );

    ...
}

也就是说，定义一些默认属性值，这些值将应用于所有属性定义，除非被覆盖。

Answer 1

听起来您想编写一些自定义属性声明，以提供一些默认选项。这在 Moose::Cookbook::Extending::Recipe1 中有介绍，例如:

package MyApp::Mooseish;

use Moose ();
use Moose::Exporter;

Moose::Exporter->setup_import_methods(
    install     => [ qw(import unimport init_meta) ],
    with_meta   => ['has_table'],
    also        => 'Moose',
);

sub has_table
{
    my ($meta, $name, %config) = @_;

    $meta->add_attribute(
        $name,

        # overridable defaults.
        is => 'rw',
        isa => 'Value', # any defined non-reference; hopefully the caller
                        # passed their own type, which will override
                        # this one.
        # other options you may wish to supply, or calculate based on
        # other arguments passed to this function...

        %config,
    );
}

然后在你的类里面:

package MyApp::SomeObject;

use MyApp::Moosish;

has_table => (
    # any normal 'has' options;
    # will override the defaults.
);

# remaining class definition as normal.