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12647 :: Avoid using a global variable and double definition to define a proc()

• zack (orginal) [2025-01-13T14:40:22+01:00] view original

  Currently, I have this in a init.nim file :

  
  var CreateNS*: proc(name: cstring):cint{.cdecl.}
  
  type Ts = object
      t_CreateNS*: proc(name: cstring):cint{.cdecl.}
  
  var tPtr{.importc: "t_Ptr", header: "my1.h".} : ptr Ts
  proc tInitS(v: cstring): cstring{.cdecl, importc: "t_InitS", header: "my2.h".}
  
  proc InitS*(v: cstring): cstring{.cdecl.} =
    let init = tInitS(v)
    CreateNS = tPtr.t_CreateNS
    return init
  Run

  My main.nim file :

  
  proc Init(): cint {.exportc, dynlib.} =
    
    if InitS("1.0") == nil:
      return 0
    
    # Call function declared in init.nim
    let ns = CreateNS("foo")
    # do something ...
    return 1
  Run

  To declare CreateNS in nim.init file, do I have to use a global variable ?

  How can I avoid rewriting the arguments a second time, one in my global variable CreateNS and the other in the properties of my type Ts ?

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• SpotlightKid (orginal) [2025-01-13T16:22:04+01:00] view original

  Not sure whether I fully understand the problem, but if you are trying to define a proc (method), which operates on Ts object instances, you don't do that within the type but just define a proc, which takes a Ts as the first argument.

  https://nim-lang.org/docs/tut2.html#object-oriented-programming-method-call-syntax

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• zack (orginal) [2025-01-14T11:16:39+01:00] view original

  ok if you didn't understand it was because my question wasn't clear.

  
  proc InitS*(v: cstring): cstring{.cdecl.} =
    let init = tInitS(v)
    CreateNS = tPtr.t_CreateNS
    #          ^^^
    return init
  Run

  To call this tPtr.t_CreateNS , I have to declare this global variable CreateNS ? is there another solution ?

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• blackmius (orginal) [2025-01-14T15:30:19+01:00] view original

  what error does it print? when you trying to call tPtr.t_CreateNS?

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• zack (orginal) [2025-01-14T15:59:31+01:00] view original

  no error @blackmius, my code works , I just want to know if I can avoid using global variables.

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• Araq (orginal) [2025-01-14T16:47:44+01:00] view original

  Yes, you can just call it directly via tPtr.t_CreateNS("foo"), no need for a global proc pointer.

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• zack (orginal) [2025-01-16T16:06:51+01:00] view original

  Thanks @Araq, I tried as you suggested but I got errors when compiling my header file my1.h.

  my1.h:54:7: error: expected ';' before 'int'

  my1.h:58:7: error: expected ';' before 'const'

  I've also tried to create a type, I like the idea (I don't know if it's possible) like this :

  
  type myproc = proc(name: cstring):cint{.cdecl.}
  var CreateNS*: myproc
  
  type Ts = object
      t_CreateNS*: myproc
  Run

  No compilation problems, but I have a seg fault when I load my xxx.dll.

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• zack (orginal) [2025-01-20T09:22:20+01:00] view original

  Now that I've made a little more progress, I'd like to know if I can simplify it further, still with the aim of avoiding using a global variable and code duplication.

  Finally, I've managed to make my code work by declaring a type :

  
  type myproc = proc(name: cstring):cint{.cdecl.}
  var CreateNS*: myproc
  
  type Ts = object
      t_CreateNS: myproc
  
  proc InitS*(v: cstring): cstring{.cdecl.} =
    CreateNS = tPtr.t_CreateNS
    return "do something"
  Run

  Instead of using this var CreateNS, I want to create a template or a procedure so that I can call it up later in my code, instead of setting it in my procedure InitS. I'd like to create a template like this :

  
  # I'm not sure if we can create a template like this...
  template CreateNS*: myproc = tPtr.t_CreateNS
  Run

  But I have this error when I call it :

  
  Error: type mismatch
  Expression: CreateNS("foo")
    [1] "foo": string
  
  Expected one of (first mismatch at [position]):
  [1] template CreateNS(): myproc
    extra argument given
  Run

  I need a little help to find out if this is possible.

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• PMunch (orginal) [2025-01-20T09:45:21+01:00] view original

  You could either do:

  
  template CreateNS(x: cstring)*: myproc = tPtr.t_CreateNS(x)
  Run

  Or you have to first call the template to get the function and then call it:

  
  CreateNs()("foo")
  Run

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• zack (orginal) [2025-01-20T14:06:22+01:00] view original

  Thanks @PMunch, I had an error in your template :

  Error: invalid indentation; an export marker '*' follows the declared identifier

  I think it was a typo. I've rewritten it like this :

  
  template CreateNS*(x: cstring): myproc = tPtr.t_CreateNS(x)
  Run

  Now I have errors, but from my header file :

  C:\dev\include\my1.h:54:7: error: expected ';' before 'int'

  C:\dev\include\my1.h:58:7: error: expected ';' before 'const'

  I called my template as you would call a procedure, I hope it's like that (I'm not too familiar with templates ).

  Except for my header file errors.

  Do I also have to declare argument(s) in my template CreateNS ?

  I'd like to avoid it (removed this (x: cstring)) because I've already declared it in my type myproc , but I don't know if it's possible.

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