greeter.php

<?php

class Greeting {
    public $message;

    function __construct($message) {
        $this->message = $message;
    }

    function format($name) {
        return $this->message.' '.$name;
    }
}

interface Greeter {
    function greet($name);
}

class StandardGreeter implements Greeter {
    private $greeting;

    function __construct(Greeting $greeting) {
        $this->greeting = $greeting;
    }

    function greet($name) {
        return $this->greeting->format($name);
    }
}

class RandomGreeter implements Greeter {
    private $greetings;

    function __construct(array $greetings) {
        $this->greetings = $greetings;
    }

    function greet($name) {
        $greeting = $this->greetings[array_rand($this->greetings)];
        return $greeting->format($name);
    }
}

$standard = new StandardGreeter(new Greeting('Hi'));
$random = new RandomGreeter([
    new Greeting('Hi'),
    new Greeting('Hello'),
    new Greeting('Yo'),
    new Greeting('Salut'),
]);

var_dump($standard->greet('Igor'));
var_dump($standard->greet('Gordon'));

var_dump($random->greet('PeeHaa'));
var_dump($random->greet('Ocramius'));
var_dump($random->greet('HamZa'));