title: "Missing parameter type for expanded function" when using _ (underscore)?
body: <p>One problem I continually run into scala is with lambda' expressions. For instance</p>
  
  <pre><code>JarBuilder.findContainingJar(clazz).foreach {userJars = userJars + _ }
  </code></pre>
  
  <p>gives me an error like:</p>
  
  <pre><code>missing parameter type for expanded function ((x$1) =&gt; userJars.$plus(x$1))
  </code></pre>
  
  <p>Yet if I do the expansion myself:</p>
  
  <pre><code>JarBuilder.findContainingJar(clazz).foreach {x =&gt; userJars = userJars + x }
  </code></pre>
  
  <p>It works fine.</p>
  
  <p>Is this a Scala bug? Or am I doing something horribly wrong?</p>