title: how to write a generic method for adding numbers
body: <p>I want to define a method to make sums between
  different type numbers:</p>
  
  <pre><code>&lt;T&gt; void add (T one, T two)
  {
      T res = one + two; 
  }
  </code></pre>
  
  <p>the above method not work because type erasure convert <code>T</code> into <code>Object</code>
  and thus the + operator is not defined on <code>Object</code>...</p>
  
  <p>How can do that?</p>
  
  <p>Thanks.</p>