title: iOS swift why two type of closure can't add to an array
body: <pre><code>let sum1 = {(a:Int, b:Int) -&gt; Int in return a + b}
  let sum2 = {(a:Float, b:Float) -&gt; Float in return a + b}
  
  var cl = [sum1, sum2]
  </code></pre>
  
  <p>Why <code>sum1</code> and <code>sum2</code> can't be added to an array?
  I know <code>sum1</code> takes two Ints return an Int, <code>sum2</code> takes two Floats return a Float, but an array can be added two different type of object, for example <code>let foo = [12, "12"]</code> is valid.</p>