title: Scala unbound placeholder parameter
body: <p>I am using the following code to meet my needs:</p>
  
  <pre><code> (1 to 5)..map(i =&gt; s"\\x${i}")  // Produces List("\\x1", "\\x2", "\\x3", "\\x4", "\\x5")
  </code></pre>
  
  <p>But I would like to use a placeholder. According to <a href="http://docs.scala-lang.org/overviews/core/string-interpolation.html" rel="nofollow">the string interpolator documentation</a> :</p>
  
  <pre><code>(1 to 5).map(s"\\x${_}")
  </code></pre>
  
  <p>should expand to:</p>
  
  <pre><code>(1 to 5).map(StringContext("\\\\x","").s(_))
  </code></pre>
  
  <p>But the latter works, not the former, which throws an <code>error: unbound placeholder parameter</code> on <code>_</code>. Why?</p>