How can I prevent Perl Moose Read-Only Attributes being set upon a call to new?

Question

I would like to simply declare a read only attribute in Moose that cannot be initialized in a call to new. So after declaring the following:

package SOD::KuuAnalyze::ProdId;

use Moose;

has 'users' => (isa => 'ArrayRef[Str]', is => "ro");

1;

I do not want the following to work:

my $prodid = SOD::KuuAnalyze::ProdId->new(users => ["one", "two"]);

users has no default, how does it ever get set? – Schwern Nov 29 '09 at 23:12 — Schwern, Nov 29 '09 at 23:12

score 15 · Accepted Answer · answered Nov 28 '09 at 23:55

15

Use the init_arg attribute configuration (see "Constructor parameters" in Moose::Manual::Attributes):

package SOD::KuuAnalyze::ProdId;
use Moose;

has 'users' => (
    isa => 'ArrayRef[Str]', is => "ro",
    init_arg => undef,    # do not allow in constructor
);
1;

answered Nov 28 '09 at 23:55

Ether

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1

This works nicely, thank you. However it fails silently. Is there a way to get it to throw an error whilst attempting ProdId->new(users => ['one','two'])? – ennuikiller Nov 29 '09 at 14:00
4

If you use MooseX::StrictConstructor, module construction will fail if any invalid or disallowed arguments are passed to the constructor. I use it in almost all my Moose classes (for the rest, I use MooseX::SlurpyConstructor which grabs all arguments that aren't used by attributes). – Ether Nov 29 '09 at 17:26

friedo · Answer 2 · 2009-11-28T23:54:54.437

4

How about

package SOD::KuuAnalyze::ProdId;

use Moose;

has 'users' => ( isa => 'ArrayRef[Str]', is => 'ro', init_arg => undef, default => sub { [ 'one', 'two' ] } );

Setting the init_arg to undef seems to be necessary to disallow setting the attribute from the constructor.

edited Nov 28 '09 at 23:54

answered Nov 28 '09 at 23:45

friedo

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How can I prevent Perl Moose Read-Only Attributes being set upon a call to new?

2 Answers2