title: Nested Swift Dictionaries
body: <p>I want to initialize a dictionary with a dictionary nested inside like this:</p>
  
  <pre><code>var a = [Int:[Int:Float]]()
  a[1][2] = 12
  </code></pre>
  
  <p>But I get an error:</p>
  
  <pre><code>(Int:[Int:Float]) does not have a member named 'subscript'
  </code></pre>
  
  <p>I've hacked at a variety of other approaches, all of them running into some kind of issue.</p>
  
  <p>Any idea why this doesn't work?</p>