title: What is _: in Swift telling me?
body: <p>What does the lone underscore mean in function definitions?</p>
  
  <p>e.g. <code>map(_:)</code></p>
  
  <p>I understand that when defining functions I can do:</p>
  
  <pre><code>func myFunc(_ string: String) { ... }
  </code></pre>
  
  <p>Would I then refer to that as <code>myFunc(_:)</code> instead of <code>myFunc(_string:)</code>, i.e. purposefully hiding the parameter name?</p>