title: Swift dictionary bug?
body: <p>So I started a project in Swift, and I've come to this problem:</p>
  
  <p>this code works:</p>
  
  <pre><code>var dictionary = ["a":"valueOfA","b":"valueOfB","c":"valueOfC"]
  println(dictionary)
  dictionary["c"] = "newValOfC"
  println(dictionary)
  </code></pre>
  
  <p>and this doesn't:</p>
  
  <pre><code>var dictionary = [:]
  dictionary = ["a":"valueOfA","b":"valueOfB","c":"valueOfC"]
  println(dictionary)
  dictionary["c"] = "newValOfC"
  println(dictionary)
  </code></pre>
  
  <p>Gives an error:</p>
  
  <pre><code>Playground execution failed: error: &lt;REPL&gt;:35:17: error: cannot assign to the result of this expression
  dictionary["c"] = "newValC"
  ~~~~~~~~~~~~~~~ ^
  </code></pre>
  
  <p>Notice that this is not a constant value</p>
  
  <p>So why doesn't the line</p>
  
  <pre><code>dictionary = ["a":"valueOfA","b":"valueOfB","c":"valueOfC"]
  </code></pre>
  
  <p>give an error?</p>