title: Generic Swift 4 enum with Void associated type
body: <p><strong>tl;dr</strong></p>
  
  <p>Is it possible to instantiate a generic Swift 4 enum member with an associated value of type <code>Void</code>?</p>
  
  <p><strong>Background</strong></p>
  
  <p>I'm using a simple <em>Result</em> enum (similar to <a href="https://github.com/antitypical/Result" rel="noreferrer">antitypical Result</a>):</p>
  
  <pre><code>enum Result&lt;T&gt; {
    case success(T)
    case error(Error?)
  }
  </code></pre>
  
  <p>Now I'd like to use this enum to represent the result of an operation which does not yield an actual result value; the operation is either <em>succeeded</em> or <em>failed</em>. For this I'd define the type as <code>Result&lt;Void&gt;</code>, but I'm struggling with how to create the Result instance, neither <code>let res: Result&lt;Void&gt; = .success</code> nor <code>let res: Result&lt;Void&gt; = .success()</code> works.</p>