title: Cannot convert value of type 'Character' to type 'String' in coercion
body: <p>In Swift, I would expect the following to be a perfectly valid code:</p>
  
  <pre><code>let snailCharacter: Character = ""
  let snailString = snailCharacter as String
  </code></pre>
  
  <p>But apparently, it produces an error:</p>
  
  <blockquote>
    <p>Cannot convert value of type 'Character' to type 'String' in coercion</p>
  </blockquote>
  
  <p>Solution to this is to use <code>String</code> initializer like this:</p>
  
  <pre><code>let snailString = String(snailCharacter)
  </code></pre>
  
  <p>I thought <code>Character</code> is kind of a subset of <code>String</code>, so that surprised me. Why is it forbidden to cast <code>Character</code> to <code>String</code>?</p>
  
  <p>I'm using Swift 4 in Xcode 9 beta 4.</p>