<?php

    interface pump {

        function get_gas();

    }

    class premium implements pump {
        function get_gas() {

            echo "chug!";
        }
    }

    class regular implements pump {
    
        function get_gas() {

            echo "chug!";
        }
    }

    class mercedes {

        function fill(premium $pump) {
            echo $pump->get_gas();
        }

    }

    class pinto {
        function fill(pump $pump) {
            echo $pump->get_gas();
        }
    }

    $pinto = new pinto;
    $pinto->fill(new premium);
    $pinto->fill(new regular);
    
    $mercedes = new mercedes;
    $mercedes->fill(new premium);
    $mercedes->fill(new regular);
?>