title: Concatenate padded strings
body: <p>I have three strings, for example "A", "B", "C".
  I have to produce the string which results from concatenating them, only the second string must be padded with whitespace to a given length.</p>
  
  <p>This was my first attempt as guided by intuition and general Scala newbiness:</p>
  
  <pre><code>val s1 = "A"
  val s2 = "B"
  val s3 = "C"
  val padLength = 20
  
  val s = s1 + s2.padTo(padLength, " ") + s3
  </code></pre>
  
  <p>which is wrong because padTo returns a SeqLike whose toString does not return the string inside but a Vector-like representation.</p>
  
  <p>What would be the best idiomatic way to do this in Scala?</p>