title: Overlapping accesses to 'urlComponents', but modification requires exclusive access
body: <p>I am trying to use the Lyft API with iOS 11 and Swift 4, and am receiving an error on the second line, which is </p>
  
  <blockquote>
    <p>Overlapping accesses to 'urlComponents', but modification requires
    exclusive access; consider copying to a local variable.</p>
  </blockquote>
  
  <p>I am unsure what this means, and how I can get around it. Any help is appreciated, thanks!</p>
  
  <pre><code>let queryItems = parameters
      .sorted { $0.0 &lt; $1.0 }
      .flatMap { components(forKey: $0, value: $1) }
  var urlComponents = URLComponents(url: mutableURLRequest.url!, resolvingAgainstBaseURL: false)
  urlComponents?.queryItems = (urlComponents?.queryItems ?? []) + queryItems //error here
  </code></pre>