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8287 :: '$' on Time can have side effect, but only if you import the whole times module

• giaco (orginal) [2021-07-31T03:03:24+02:00] view original

  I was trying to put funcs where I had procs, and I've stumbled into a curious behavior

  https://play.nim-lang.org/#ix=3uxk

  import std/[strformat]
  
  const chooseYourDestiny = 2
  
  when chooseYourDestiny == 0: # this works
    from std/times import Time
  elif chooseYourDestiny == 1: # this works
    # copypasted from times.nim
    type
      NanosecondRange* = range[0..999_999_999]
      Time* = object
        seconds: int64
        nanosecond: NanosecondRange
  else: # Error: '$' can have side effects
    import std/times
  
  type
    MyObj* = object
      timestamp*: Time
  
  func `$`*(o: MyObj): string =
    &"{o.timestamp}"
  Run

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• Araq (orginal) [2021-07-31T10:31:59+02:00] view original

  Nim devel produces:

  
  
  E:\nim\temp10.nim(26, 6) Error: '$' can have side effects
  > E:\nim\lib\pure\times.nim(2073, 20) Hint: '$' calls `.sideEffect` 'format'
  >> E:\nim\lib\pure\times.nim(2065, 6) Hint: 'format' called by '$'
  >>> E:\nim\lib\pure\times.nim(2069, 16) Hint: 'format' calls `.sideEffect` 'inZone'
  >>>> E:\nim\lib\pure\times.nim(1180, 6) Hint: 'inZone' called by 'format'
  > E:\nim\lib\pure\times.nim(2065, 67) Hint: '$' calls `.sideEffect` 'local'
  >> E:\nim\lib\pure\times.nim(1302, 6) Hint: 'local' called by '$'
  Run

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• giaco (orginal) [2021-07-31T18:02:39+02:00] view original

  I now see that the $ function in times.nim reads a global for both UTC and local convesion that breaks noSideEffect.

  Shouldn't be formatting know time to UTC or local a side effect free operation?

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