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6697 :: How to check typedesc type inside macro?

• c0ffee (orginal) [2020-08-19T16:30:50+02:00] view original

  Hello. How to check type inside macro?

  import macros
  type
    T1 = object
      s : string
  
  proc checkTypeProc( t : typedesc )=
    if t is T1:
      echo "proc: is T1"
    else:
      echo "proc: not T1"
  
  macro checkTypeMacro(t:static[typedesc]):untyped=
    if t is T1:
      result = quote do: echo "macro: is T1"
    else:
      result = quote do: echo "macro: not T1"
  
  if isMainModule:
    checkTypeProc(T1)
    checkTypeMacro(T1)
  
  # Output:
  # proc: is T1
  # macro: not T1
  Run

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• mratsim (orginal) [2020-08-19T17:41:28+02:00] view original

  With a lot of pain:

  • https://github.com/nim-lang/Nim/issues/6785
  • https://github.com/nim-lang/Nim/issues/14021
  • https://github.com/nim-lang/RFCs/issues/44

  And unfortunately typeof(t) doesn't work either.

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• c0ffee (orginal) [2020-08-26T11:44:58+02:00] view original

  Found a workaround for places where type is still accessible. Call template that wraps macro and unpacks type data into macro's arguments.

  import macros
  type
    T1 = object
      s : string
    T2 = object
  
  proc checkType_Proc( t : typedesc )=
    if t is T1:
      echo "proc: ", t, " is T1"
    else:
      echo "proc: ", t, " is not T1"
  
  macro checkType_Macro(t:static[typedesc]):untyped=
    if t is T1:
      result = quote do: echo "macro: ", $`t`, " is T1"
    else:
      result = quote do: echo "macro: ", $`t`, " is not T1"
  
  template checkType_Template(t:typedesc)=
    checkType_TemplateMacro( $`t`, t is T1 )
  
  macro checkType_TemplateMacro( typeName: static[string], isT1: static[bool] ):untyped=
    if isT1:
      result = quote do: echo "templateMacro: ", $`typeName`, " is T1"
    else:
      result = quote do: echo "templateMacro: ", $`typeName`, " is not T1"
  
  if isMainModule:
    checkType_Proc(T1)
    checkType_Proc(T2)
    echo ""
    checkType_Macro(T1)
    checkType_Macro(T2)
    echo ""
    checkType_Template(T1)
    checkType_Template(T2)
  
  # Output
  # proc: T1 is T1
  # proc: T2 is not T1
  #
  # macro: T1 is not T1
  # macro: T2 is not T1
  #
  # templateMacro: T1 is T1
  # templateMacro: T2 is not T1
  Run

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