Example of using PHP Interfaces

00_Example_Usage.php

<?php
// Example usage
if($myMessage instanceof MessageInterface){
    // Because $message implements MessageInterface, we 
    // can be absolutely sure that it has a send() method
    // so don't have to care what it does when sending,
    // just that it has the capability to send
    $message->send();
}

EmailMessage.php

<?php

lass EmailMessage implements MessageInterface
{
    protected $content;
    protected $recipient;
    protected $subject = 'Hello World';

    public function send(){
        mail($this->recipient,$this->subject,$this->content);
    }

    public function setRecipient($recipient){
        if(! isEmailAddress($recipient)){
            throw new Exception("{$recipient} is not a valid email address");
        }
        $this->recipient = $recipient;
    }

    public function setContent($content){
        $this->content = $content;
    }
}

MessageInterface.php

<?php
interface MessageInterface 
{
    public function setRecipient($recipient);
    public function setContent($content);
    public function send();
}

TextMessage.php

<?php
class TextMessage implements MessageInterface
{

    protected $recipient;
    protected $content;

    protected $smsApi;

    public function send(){
        $smsApi->sendText($this->recipient,$this->content);
    }

    public function setRecipient($recipient){
        if(! isPhoneNumber($recipient)){
            throw new Exception("{$recipient} is not a valid UK phone number!")
        }
        $this->recipient = $recipient;
    }

    public function setContent($content){
        if(strlen($content) > 140 ){
            throw new Exception("Content is too long to send as a txt message!");
        }
        $this->content = content;
    }

}