has pizza => (
        is     => 'ro',
        isa    => 'Pizza',
        writer => '_pizza',
    );

##</code><code>##

    has 'pizza' , 
        is     => 'ro',
        isa    => 'Pizza',
        writer => '_pizza',
    ;

##</code><code>##

    has pizza => {
        is     => 'ro',
        isa    => 'Pizza',
        writer => '_pizza',
    };