title: Scala strange implicit boxing conversion error
body: <p>Can someone tell me why the following does not work?</p>
  
  <pre><code>object TestObject {
      def map(f: (Double, Double) =&gt; Double, x2: Array[Double]) = {
          val y = x2.zip( x2 )
          val z = y.map(f)
          z
      }
  }
  </code></pre>
  
  <p>Produces this error:</p>
  
  <pre><code>type mismatch; found : (Double, Double) =&gt; Double required: ((Double, Double)) =&gt; ?
  </code></pre>