title: Scala Get All Fields without default value
body: <p>I have the following code:</p>
  
  <pre><code>case class Person(name: String, age: Int = 0)
  
  def extractFieldNames[A](implicit m: Manifest[A]): Array[String] =
      m.runtimeClass.getDeclaredFields.map(_.getName)
  
  extractFieldNames[Person]
  // should return Array("name", "age")
  </code></pre>
  
  <p>But what if I want to exclude age because of its default parameter? How would I do this?</p>