use strict;
use warnings;
use Types::Standard -types;
use MooX::Struct Cat    => ['$name'];
use MooX::Struct Litter => ['@cats' => [ isa => ArrayRef[InstanceOf[Cat]] ]];

my $cat1   = Cat->new(name=>'Garfield');
my $cat2   = Cat->new(name=>'Felix');
my $litter = Litter->new(cats => [$cat1, $cat2, 1]);