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4558 :: template/macro to create function/variant?

• oyster (orginal) [2019-01-15T07:06:10+01:00] view original

  In freebasic, for code

  
  #macro DeclareEx(_name_)
  declare function _name_##ExNew(byval x as long, byval y as long, byval w as long, byval h as long, byval title as const zstring ptr=0) as _name_##Ex ptr
  declare sub      _name_##ExDelete         (byref ex as _name_##Ex ptr)
  #endmacro
  Run

  if we call DeclareEx(Fl_Button) then we get the 2 procedure

  
  declare function Fl_ButtonExNew(byval x as long, byval y as long, byval w as long, byval h as long, byval title as const zstring ptr=0) as Fl_Button ptr
  declare sub      Fl_ButtonExDelete         (byref ex as Fl_ButtonEx ptr)
  Run

  how can we do that in nim? I have tried template and macro.

  template Kitten*(name: string)  =
    var name_1 = "Mike"
  
  
  Kitten("q")
  echo q_1
  Run

  says

  
  a.nim(6, 6) Error: undeclared identifier: 'q_1'
  Run

  at same time

  macro Kitten*(name: string) : untyped  =
    var name_1 = "Mike"
  
  
  Kitten("q")
  echo q_1
  Run

  says

  
  a.nim(2, 7) Hint: 'name_1' is declared but not used [XDeclaredButNotUsed]
  a.nim(6, 6) Error: undeclared identifier: 'q_1'
  
  Run

  thnaks

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• rayman22201 (orginal) [2019-01-15T07:37:11+01:00] view original

  This should do what you want:

  template Kitten* (name: untyped) = # The type is untyped here, not string
    var `name 1` {.inject.} = "Mike" # note: no underscore character, but a space instead.
    
    # macros and templates are hygenic, so we need the inject pragma to allow the template to
    # "dirty" the program by inserting a new symbol into it.
  
  Kitten(q)
  # note: no quotes here. It's an identifier, not a string.
  # This corresponds to the "untyped" above.
  echo q_1
  Run

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