{
        package Grid;;
        use Moose;
        use Moose::Util::TypeConstraints;

        # coerce an 'ArrayRef[ArrayRef[Cell]]' struct provided by the caller into an 'ArrayRef[Row]' type
        subtype 'A::Row' => as 'ArrayRef[Row]';
        coerce 'A::Row' => from 'ArrayRef[ArrayRef[Cell]]' => via { [ map {Row->new( row => $_ )} @$_ ] };

        # coerce an 'ArrayRef[Cell]' struct provided by the caller into a 'Row' type
        coerce 'Row' => from 'ArrayRef[Cell]' => via { Row->new( row => $_ ) };

        has 'grid' => (
                traits          => ['Array'],
                is              => 'ro',
                isa             => 'A::Row',
                required        => 1,
                default         => sub { [] },
                coerce          => 1,
                handles         => {
                        addRow => 'push',
                        getRow  => 'get',
                        allRows => 'elements',
                },
        );
}