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3627 :: Compiler crash when pointers to generics from template

• lucian (orginal) [2018-03-11T00:12:43+01:00] view original

  I have stumbled this error: "nim c main" gives "SIGSEGV: Illegal storage access. (Attempt to read from nil?)" on machine setup: Nim Compiler Version 0.18.0 [Windows: amd64], "uname -a" -> MINGW64_NT-10.0 <name> 2.9.0(0.318/5/3) 2017-09-13 23:16 x86_64 Msys

  Simple sources are as:

  
  # lib1.nim
  proc PresentModeA*[T:string|seq[byte]](d: T) =
      echo "A Presenting: ", $d[0]
  Run

  
  #lib2.nim
  
  proc PresentModeB*[T:string|seq[byte]](d: T) =
      echo "B Presenting: ", $d[0]
  Run

  
  #main app
  import
      os, sequtils, strutils,
      lib1, lib2
  
  type
      modes = enum
          typeA, tyepB
  var
      mode = typeA
  
  template PresentGeneric(s: typed) =
      var dispatcher = @[PresentModeA, PresentModeB]
      dispatcher[mode.ord](s)
  
  proc main() =
      # 'mode' is really dependant on optargs
      
      let data = @[0x00.byte, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07]
      PresentGeneric(data)
      
      let text = "Something to shout about."
      PresentGeneric(text)
  
  main()
  Run

  Is this design supported or should avoid generics pointers?

  Thank you.

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• Araq (orginal) [2018-03-11T13:38:34+01:00] view original

  Compiler bug aside, you need to instantiate the procs, like @[presentModeA[string], presentModeB[string]].

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• lucian (orginal) [2018-03-11T22:13:46+01:00] view original

  Great, this works:

  
  var dispatcher = @[PresentModeA[type(s)], PresentModeB[type(s)]]
  Run

  what doesn't work though is if the implementations of PresentMode_A/B() are then expanded separately for other types:

  
  proc PresentModeA*[T:string|seq[byte]](d: T) = ...
  proc PresentModeA*(d: bool) = ...
  Run

  the error in main being: Error: cannot instantiate: 'PresentModeA[type(some_bool_var)]'

  But that would be stretching it I suppose. So I'm happy with the single implementation, as long as I remember the limitation.

  Thanks again.

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• mratsim (orginal) [2018-03-12T08:35:26+01:00] view original

  Probably because the overloaded PresentModeA is not generic so you can't use this syntax PresentModeA[Foo], try with that:

  proc PresentModeA*[T: bool](d: T) = ...
  Run

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