<?php
interface read_file {
    function open($file_name);
    function read($bytes);
    function close();
}

class rf implements read_file {
    private $fp;

    function open($file_name) { $this->fp = fopen($file_name, "r"); }
    function read($bytes) { return fread($this->fp, $bytes); }
    function close() { fclose($this->fp); }
}

$f = new rf();
/* ensure that object inside $ implements read_file interface */
if ($f instanceof read_file) {
    $f->open(__FILE__);
    echo $f->read(4);
    $f->close();    
}
?>