title: Scala `view`: `force` is not a member of `Seq`
body: <p>It appears that applying <code>map</code> and <code>filter</code> somehow converts a <code>view</code> into a <code>Seq</code>. The <a href="http://www.scala-lang.org/docu/files/collections-api/collections_42.html" rel="noreferrer">documentation</a> contains this example:</p>
  
  <pre><code>&gt; (v.view map (_ + 1) map (_ * 2)).force
  res12: Seq[Int] = Vector(4, 6, 8, 10, 12, 14, 16, 18, 20, 22)  
  </code></pre>
  
  <p>But if I do something similar, I get an error:</p>
  
  <pre><code>&gt; val a = Array(1,2,3)
  &gt; s.view.map(_ + 1).map(_ + 1).force
  &lt;console&gt;:67: error: value force is not a member of Seq[Int]
  </code></pre>
  
  <p>It seems that if I <code>map</code> over an <code>Array</code> <code>view</code> more than once the <code>SeqView</code> becomes a <code>Seq</code>.</p>
  
  <pre><code>&gt; a.view.map(_+1)
  res212: scala.collection.SeqView[Int,Array[Int]] = SeqViewM(...)
  &gt; a.view.map(_+1).map(_+1)
  res211: Seq[Int] = SeqViewMM(...)
  </code></pre>
  
  <p>I suspect this behavior may have something to do with <code>Array</code> being a mutable collection, as I cannot replicate this behavior with <code>List</code> or <code>Vector</code>. I can however <code>filter</code> the <code>Array</code> <code>view</code> as many times as I like.</p>