title: Scala type members variance
body: <p>Consider this short snippet:</p>
  
  <pre><code>trait Table[+A] {
    type RowType = Seq[A]
  }
  </code></pre>
  
  <p>Scala 2.11.7 compiler gives the following error:</p>
  
  <pre><code>covariant type A occurs in invariant position in type Seq[A] of type RowType
  </code></pre>
  
  <p>Why is <code>A</code> considered to be in invariant position in <code>Seq[A]</code> while <code>Seq</code> itself is defined as <code>trait Seq[+A]</code>?</p>
  
  <p>Also, could you please provide a use case demonstrating possible issues with this type definition if we ignore the error?</p>