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10282 :: macro - global var behaviour

• mantielero (orginal) [2023-06-18T16:26:22+02:00] view original

  I think I might be missing a point with the following macro. It aims to create a proc and I want it to create a variable in the global scope:

  import macros
  
  macro testing(name:static[string]; value:int): untyped =
    var tmp = newIdentNode(name)
    result = quote do:
      proc myProc() =
         var `tmp` {.global.} = `value`
  
  var id {.compiletime.} = "hola"
  testing(id, 2)
  
  myProc()
  
  echo hola  # <--FAILS
  Run

  On the other hand, the following works:

  import macros
  
  
  macro testing(name:static[string]; value:int): untyped =
    var tmp = newIdentNode(name)
    result = quote do:
      #proc myProc() =
      var `tmp` {.global.} = `value`
  
  var id {.compiletime.} = "hola"
  testing(id, 2)
  
  #myProc()
  
  echo hola  # <--FAILS
  Run

  Maybe I am not understanding the purpose of {.global.}.

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• Yardanico (orginal) [2023-06-18T16:31:14+02:00] view original

  From https://nim-lang.org/docs/manual.html#pragmas-global-pragma:

  
  The global pragma can be applied to a variable within a proc to instruct the compiler to store it in a global location and initialize it once at program startup.
  Run

  So it's just a way to have a variable initialize only once without adding a separate variable for caching.

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• mantielero (orginal) [2023-06-18T16:38:55+02:00] view original

  So I misunderstood is purpose. Thanks for the clarification.

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