title: Struct does not conform to protocol 'Hashable'
body: <p>I wish to create an array which will only hold unique instances of a struct:</p>
  
  <pre><code>  var vowelSet: Set&lt;NotificationStruct&gt; 
  </code></pre>
  
  <p>Here is my struct:</p>
  
  <pre><code>struct NotificationStruct{
      let dateHeader: String
      let sensorName: String
      let message: String
      let time: String
  }
  </code></pre>
  
  <p>yet I keep getting the error: "does not conform to protocol 'Hashable'"
  here is what I tried:</p>
  
  <pre><code> struct NotificationStruct&lt;T: Hashable&gt;{
  </code></pre>