title: Cannot convert String to Double in Swift
body: <p>I have a dictionary as a response from server:</p>
  
  <pre><code>{ 
    "gross_price" = "6.00";
    "gross_price_total" = "6.00";
    "guests_count" = 1;
  }
  </code></pre>
  
  <p>Then I try:</p>
  
  <pre><code> let x = dictionary["gross_price_total"] as? Double
   let y = dictionary["gross_price_total"]!
   println("result: \(x) \(y)")
  </code></pre>
  
  <p>As an output I get:</p>
  
  <pre><code>result: nil 6.00
  </code></pre>
  
  <p>Why? Is it not a <code>Double</code>?</p>
  
  <p>It results that my final code doesn't work:</p>
  
  <pre><code>if let grossPriceTotal = dictionary["gross_price_total"] as? Double {
      println("final result: \(grossPriceTotal)")
  }
  </code></pre>