title: Xcode force me to use contains(where:) instead of contains()
body: <p>I wanna check if in an array have already contained an item or not so I use to like this:</p>
  
  <pre><code>let fItem = FilterItem(key: String(describing: key), value: valueStr)
  if self.filter?.filters?.contains(fItem){
      //remove the item if contains, append if not
  }
  </code></pre>
  
  <p>For more information, the <code>self.filter?.filters?</code> is an array:</p>
  
  <pre><code>var filters: [FilterItem]? = []
  </code></pre>
  
  <p>And the <code>FilterItem</code> is a struct:</p>
  
  <pre><code>struct FilterItem {
      var key: String;
      var value: String;
  }
  </code></pre>
  
  <p>But Xcode forced me to use <code>contains(where:..)</code> instead of <code>contains()</code> with error: <code>Missing argument label 'where:' in call</code>. Why?</p>