title: Why do Ruby people say they don't need interfaces?
body: <p>Does ruby have something different to other OOP languages (eg: PHP) that makes interfaces useless? Does it have some kind of replacement for this?</p>
  
  <p>Edit:</p>
  
  <p>Some clarifications:</p>
  
  <ul>
  <li><p>In other languages (eg: PHP), you don't "need" interfaces (they are not mandatory at code level). You use them to make a contract, to improve the architecture of the software. Therefore, the affirmation 'in ruby you don't need interfaces / in other languages you need interfaces because XXX' is false.</p></li>
  <li><p>No, mixins are not interfaces, they are a complete different thing (PHP 5.4 implements mixins). Have you even used interfaces?</p></li>
  <li><p>Yes, PHP is OOP. Languages evolve, welcome to the present.</p></li>
  </ul>