title: Using SKActionTimingFunction in Sprite Kit
body: <p>I have a moving action in Sprite Kit, and I'm controlling the transition like this:</p>
  
  <pre><code>mySKAction.timingMode = SKActionTimingMode.EaseIn
  </code></pre>
  
  <p>I want to create a custom transition using <code>SKActionTimingFunction</code>, but I can't figure out how. Based on the documentation, I think a simple linear transition would look something like this:</p>
  
  <pre><code>func myTransition(time: Float) -&gt; Float {
      return time
  }
  
  mySKAction.timingFunction = myTransition()
  </code></pre>
  
  <p>But I just can't make it work. It displays an error: if I put in time as the function's parameter as the documentation suggests, I get '(UnsafeMutablePointer) -> time_t' is not convertible to 'Float'.</p>