title: Flatten an Array of Arrays in Swift
body: <p>Is there a counterpart in Swift to <code>flatten</code> in Scala, Xtend, Groovy, Ruby and co?</p>
  
  <pre><code>var aofa = [[1,2,3],[4],[5,6,7,8,9]]
  aofa.flatten() // shall deliver [1,2,3,4,5,6,7,8,9] 
  </code></pre>
  
  <p>of course i could use reduce for that but that kinda sucks</p>
  
  <pre><code>var flattened = aofa.reduce(Int[]()){
      a,i in var b : Int[] = a
      b.extend(i)
      return b
  }
  </code></pre>