title: Scala: How to find out which CanBuildFrom implementation is used for StringOps.map
body: <p>I'm learning Scala by working the exercises from the book "Scala for the Impatient". One questions asks:</p>
  
  <blockquote>
    <p>The result of <code>"abc".map(_.toUpper)</code> is a <code>String</code>, but the result of
    <code>"abc".map(_.toInt)</code> is a <code>Vector</code>. Find out why.</p>
  </blockquote>
  
  <p>After reading "<a href="http://docs.scala-lang.org/overviews/core/architecture-of-scala-collections.html" rel="nofollow">The Architecture of Scala Collections</a>", I think this is because of different <code>CanBuildFrom</code> implicit implementations chosen. How can I find out which ones are chosen for the above expressions?</p>