title: Check if the user pass the value or it used the default optional parameter in Swift function
body: <p>This is not a common case, I want to know if the user passed the value or it used the default value in Swift. For example </p>
  
  <pre><code>func test(firstThing: Int? = nil) {
      if firstThing.isNil {
          if // firstThing used the default value {
              print("default")
          } else {
              print("nil ingresed")
          }
       }
  }
  </code></pre>
  
  <p>It should have the following behaviour:
      test() // "default"
      test(firstThing: nil) // "nil ingresed"</p>