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4096 :: Problem with .isNil for string inside of macro

• Stefan_Salewski (orginal) [2018-08-02T08:01:29+02:00] view original

  proc t(i: int): string =
    if i != 0: return "OK"
  
  echo t(1)
  let x = t(0)
  echo x
  if x == nil: echo "is nil"
  if x.isNil: echo "is nil"
  if x == "": echo "is nil"
  
  macro mconnect(arg: typed): untyped =
    let sci = t(0)
    if sci.isNil:
      echo "nil1"
    if sci == nil:
      echo "nil2"
    if sci == "":
      echo "nil3"
  
  mconnect(0)
  Run

  
  $ nim c t.nim
  Hint: used config file '/home/stefan/Nim/config/nim.cfg' [Conf]
  Hint: system [Processing]
  Hint: t [Processing]
  nil2
  nil3
  Hint:  [Link]
  Hint: operation successful (12093 lines compiled; 0.131 sec total; 16.324MiB peakmem; Debug Build) [SuccessX]
  Run

  So there is no "nil1" output, indicating sci.isNil is not true as expected (by me).

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• DeletedUser (orginal) [2018-08-02T08:54:50+02:00] view original

  You're using the devel branch, which I think is currently in the process of eliminating nil strings and removing isNil. Maybe the nil literal is currently being used as an alias for empty string/seq right now and that's why 2 works and not 3.

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• Stefan_Salewski (orginal) [2018-08-02T09:15:27+02:00] view original

  Yes, I heard that.

  I switched to devel because some people complained about gintro not working with devel any more.

  Will .isNil and "x == nil" be an alias for "x == "" " in future, or will it be eliminated, so giving compiler errors?

  Note that .isNil is working fine in regular code, but not in macros any more.

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