title: Define variable type Ruby in function declaration
body: <p>How can i declare variable type in function definition?</p>
  
  <p>In the next code:</p>
  
  <pre><code>def f(a, b)
  #...
  end
  </code></pre>
  
  <p>I can forget with what type it works with. How can i declare that it is a fixnum? Thanks</p>