title: missing parameter type for expanded function The argument types of an anonymous function must be fully known. (SLS 8.5) Expected type was:?
body: <p>When I use Spark2.0  Dataset and DataFrame to read datas ,the code is :</p>
  
  <pre><code> def func(docs: DataFrame): RDD[(String, String)] = {
     docs.select("id", "title").map{
       case Row(id: String, title: String) =&gt; (id, title)
   }}
  </code></pre>
  
  <p>but the compile error is </p>
  
  <pre><code>missing parameter type for expanded function The argument types of an anonymous function must be fully known. (SLS 8.5) Expected type was: ?
  </code></pre>
  
  <p>and i also try the way</p>
  
  <p><code>def func(docs: DataFrame): RDD[(String, String)] = {
     docs.select("id", "title").map{val =&gt; val match{
       case Row(id: String, title: String) =&gt; (id, title)
   }}}</code>  but this is not work !   the error on the 'val' is :</p>
  
  <pre><code>◾missing parameter type
  </code></pre>
  
  <p>how can i slove this !</p>