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;

##</code><code>##

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;