Hi K.D.J.

Here's how I do it in Moo. The Type::Tiny libs work seamlessly with Moose, I believe, so this code should Moosify as is.

package My::Types;

use strict; use warnings;

use parent 'Type::Library';
use Type::Utils; # gets you sugar, 'declare' etc.
use Types::Standard qw/ Maybe Str Int /;

declare 'OptInt', as Maybe[Int], message {'must be integer or nothing'
+};
declare 'OptStr', as Maybe[Str], message {'must be string or nothing'}
+;

1;
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package My::Class;

use Moo;
use My::Types qw/ :all /;

has optional_numeric_arg => ( is => 'ro', isa => OptInt );
has optional_string_arg  => ( is => 'ro', isa => OptStr );

1;
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Note that as an added benefit this also gets you an importable is_TypeName function for each type you declare that can be used anywhere for simple data validation.

( I believe I first learned of these techniques in This Advent Calendar article. )

Hope this helps...