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27 Annotations

Sample run of chapter's interpreter examples

• 27.1 Why have annotations?
• 27.2 Syntax of annotations
• 27.3 Standard annotations
• 27.4 Conclusion

27.1 Why have annotations?

27.2 Syntax of annotations

// In file annotations/Deprecation1.scala

  @deprecated def bigMistake() = //...


// In file annotations/Misc.scala

  @deprecated class QuickAndDirty {
    //...
  }


// In file annotations/Misc.scala

  (e: @unchecked) match {
    // non-exhaustive cases...
  }


  @cool val normal = "Hello"
  @coolerThan(normal) val fonzy = "Heeyyy"


  scala> import annotation._
  import annotation._

  scala> class strategy(arg: Annotation) extends Annotation
  defined class strategy

  scala> class delayed extends Annotation
  defined class delayed

  scala> @strategy(@delayed) def f() = {} 
  <console>:1: error: illegal start of simple expression
         @strategy(@delayed) def f() = {}
                   ^
  scala> @strategy(new delayed) def f() = {}
  f: ()Unit


  

27.3 Standard annotations

  @deprecated def bigMistake() =  //...


// In file annotations/Deprecation2.scala

  @deprecated("use newShinyMethod() instead")
  def bigMistake() =  //...


  $ scalac -deprecation Deprecation2.scala 
  Deprecation2.scala:33: warning: method bigMistake in object
  Deprecation2 is deprecated: use newShinyMethod() instead
      bigMistake()
      ^
  one warning found


// In file annotations/Native.scala

  @native
  def beginCountdown() = {}


  

27.4 Conclusion