#! perl
use strict;
use warnings;
use Data::Dump;

package Square
{
    use Moose;
    use namespace::autoclean;

    has queen_is_present =>
    (
        is      => 'rw',
        isa     => 'Bool',
        default =>  0,
    );

    has is_threatened =>
    (
        is      => 'rw',
        isa     => 'Int',
        default =>  0,
    );

    no Moose;
    __PACKAGE__->meta->make_immutable;
}

use enum qw(
               :Rank_=0 r1 r2 r3 r4 r5 r6 r7 r8
               :File_=0  a  b  c  d  e  f  g  h
           );

my @board;

for my $rank (Rank_r1 .. Rank_r8)
{
    $board[$rank][$_] = Square->new() for File_a .. File_h;
}

$board[1][2]->is_threatened(7);        # OK:            7   is     an 'Int'
dd @board;
$board[3][4]->is_threatened('foo');    # Runtime error: foo is not an 'Int'