title: Checking if `if let` is nil
body: <p>I have an app where I'm currently using the <a href="https://github.com/jrendel/SwiftKeychainWrapper" rel="nofollow" title="SwiftKeychainWrapper">SwiftKeychainWrapper</a>. Below is the code I have which checks if <code>retrievedString</code> is <code>nil</code>. However I'm still getting <code>retrievedString: nil</code> in the console. </p>
  
  <p>Shouldn't the code in the if-let statement not run, or am I using/understanding if-let incorrectly?</p>
  
  <p>With the given example, what's the correct way to use if-let to unwrap my optional value?</p>
  
  <pre><code>if let retrievedString: String? = KeychainWrapper.stringForKey("username") {
      print("retrievedString: \(retrievedString)")
      //value not nil
  } else {
      //Value is nil
  }
  </code></pre>