title: Spark Dataset select with typedcolumn
body: <p>Looking at the <code>select()</code> function on the spark DataSet there are various generated function signatures:</p>
  
  <pre><code>(c1: TypedColumn[MyClass, U1],c2: TypedColumn[MyClass, U2] ....)
  </code></pre>
  
  <p>This seems to hint that I should be able to reference the members of MyClass directly and be type safe, but I'm not sure how...</p>
  
  <p><code>ds.select("member")</code> of course works .. seems like <code>ds.select(_.member)</code> might also work somehow?</p>