title: What is the scala notation written as _:type?
body: <p>I'm following the scala tutorial.</p>
  
  <p>In function literal, it has a following notation:</p>
  
  <pre><code>(_ : *type*) =&gt; println("pressed")
  </code></pre>
  
  <p>For example, </p>
  
  <pre><code>(_ : Int) =&gt; println("pressed")
  </code></pre>
  
  <p>In this notation, I couldn't understand what <strong>(_ : <em>type</em>)</strong> means.</p>