title: How do you make code reusable?
body: <p>Any code can be reused in a way or an other, at least if you modify the code. Random code is not very reusable as such. When I read some books, they usually say that you should explicitly make the code reusable by taking into account other situations of code usage too. But certain code should not be an omnipotent all doing class either.</p>
  
  <p>I would like to have reusable code that I don't have to change later. How do you make code reusable? What are the requirements for code being reusable? What are the things that reusable code should definitely have and what things are optional?</p>