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4591 :: is it possible to write a converter which only convert 0 to nil

• oyster (orginal) [2019-01-25T14:56:11+01:00] view original

  The C code

  int setCallback(Fl_Widget* wgt, Fl_Callback *cb, void *pdata=NULL, int num=1);
  Run

  can be translated into

  proc setCallback*(wgt: ptr Fl_Widget; cb: ptr Fl_Callback;
                               pdata: pointer = nil; num: cint = 1): cint
  Run

  Instead of

  setCallback(wgt,  cb, nil, 2)
  Run

  I want to call the function as

  setCallback(wgt,  cb, 0, 2)
  Run

  I have tried use

  
  converter toNil(x: int=0): type(nil) = nil
  Run

  but

  
  Error: invalid type: 'nil' in this context: 'proc (x: int): nil' for proc
  Run

  so, is it possible to write a convertor which actually convert number zero only to nil? thanks

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• Stefan_Salewski (orginal) [2019-01-25T16:44:23+01:00] view original

  In Nim you can define procs with same name but different parameter list, so this compiles:

  type
    Fl_Widget = int
    Fl_Callback = int
  
  proc setCallback*(wgt: ptr Fl_Widget; cb: ptr Fl_Callback;
                               pdata: pointer = nil; num: cint = 1): cint = discard
  
  proc setCallback*(wgt: ptr Fl_Widget; cb: ptr Fl_Callback;
                               pdata: int = 0; num: cint = 1): cint =
    var hhh: pointer = cast[pointer](pdata)
    #setCallback(wgt,  cb, pointer(pdata), num)
    setCallback(wgt,  cb, hhh, num)
  
  var wgt: ptr Fl_Widget
  var  cb: ptr Fl_Callback
  discard setCallback(wgt,  cb, nil, 2)
  discard setCallback(wgt,  cb, 0, 2)
  Run

  The problem in this case may be that size of cint is not equal to size of pointer. You may use int as parameter type, as size of int is size of pointer in Nim. Direct type conversion with pointer(mycint) seems not to work, so I used a cast with additional variable. You may test it, maybe you have to use a when statement to decide if size(cint) is smaller than size(pointer) and execute different code. Note that your topmost "C" code seems to be C++, as C generally has no defaults for parameters.

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• oyster (orginal) [2019-01-26T03:48:10+01:00] view original

  hi, Stefan_Salewski You find the lazy bone in me exactly, thank you for the explaination. Now the original Code( in FreeBASIC )

  
  #include once "fltk-c. bi"
  
  sub QuitCB cdecl (byval self as Fl_Widget ptr,byval userdata as any ptr)
   flMessageTitle("QuitCB called !")
   if flChoice("Do you really want to exit ?","no","yes") then
   Fl_WindowHide Fl_WidgetWindow(self)
   end if
  end sub
  
  '
  ' main
  '
  var win = Fl_WindowNew(640,480)
  var bar = Fl_Menu_BarNew(0,0,Fl_WidgetGetW(win),25) ' Fl_ALIGN_TEXT_OVER_IMAGE
  Fl_WindowShow win ' <- must be shown for drawing
  
  ' params: menu, mnuPath ,mnuLabel , image ,[shortcut],[@MenuCB],IMAGE_ALIGN , LABEL_ALIGN
  Fl_Menu_AddImageLabel(bar,"File/Test1","Test" ,"media/8x8. png", , ,Fl_ALIGN_IMAGE_OVER_TEXT, Fl_ALIGN_LEFT)
  Fl_Menu_AddImageLabel(bar,"File/Test2","Test" ,"media/8x8. png", , ,Fl_ALIGN_TEXT_OVER_IMAGE, Fl_ALIGN_RIGHT)
  
  Fl_Menu_AddImageLabel(bar,"File/Open1","Open. . . ","media/16x16. png", , ,Fl_ALIGN_IMAGE_NEXT_TO_TEXT, Fl_ALIGN_LEFT or FL_ALIGN_TOP)
  Fl_Menu_AddImageLabel(bar,"File/Open2","Open. . . ","media/16x16. png", , ,Fl_ALIGN_IMAGE_NEXT_TO_TEXT, Fl_ALIGN_CENTER)
  Fl_Menu_AddImageLabel(bar,"File/Open3","Open. . . ","media/16x16. png", , ,Fl_ALIGN_IMAGE_NEXT_TO_TEXT, Fl_ALIGN_RIGHT or FL_ALIGN_BOTTOM)
  
  Fl_Menu_AddImageLabel(bar,"File/Exit3","Exit" ,"media/exit-2_32x32. png" ,,@QuitCB,Fl_ALIGN_TEXT_NEXT_TO_IMAGE, Fl_ALIGN_RIGHT or FL_ALIGN_BOTTOM)
  Fl_Menu_AddImageLabel(bar,"File/Exit2","Exit" ,"media/application-exit-4_32x32. png",,@QuitCB,Fl_ALIGN_TEXT_NEXT_TO_IMAGE, Fl_ALIGN_CENTER)
  Fl_Menu_AddImageLabel(bar,"File/Exit1","Exit" ,"media/exit-2_32x32. png" ,,@QuitCB,Fl_ALIGN_TEXT_NEXT_TO_IMAGE, Fl_ALIGN_LEFT or FL_ALIGN_TOP)
  
  
  
  Fl_Run
  
  Run

  can be written with my nim binding as

  
  import fltk_main
  import fltk_tools
  
  proc QuitCB (self: ptr Fl_Widget, userdata: pointer) {.cdecl.} =
      flMessageTitle("QuitCB called !")
      if flChoice("Do you really want to exit ?","no","yes") > 0 :
          Fl_WindowHide Fl_WidgetWindow(self)
  
  
  var win = Fl_WindowNew(640,480)
  var bar = Fl_Menu_BarNew(0,0,Fl_WidgetGetW(win),25)              #' Fl_ALIGN_TEXT_OVER_IMAGE
  Fl_WindowShow win #' <- must be shown for drawing
  
  #~ ' params:            menu, mnuPath,mnuLabel, image,[shortcut],[MenuCB],IMAGE_ALIGN, LABEL_ALIGN
  # you can use 0 or nil for the dummy MenuCB
  Fl_Menu_AddImageLabel(bar, "File/Test1", "Test", "media/8x8.png", 0, 0, Fl_ALIGN_IMAGE_OVER_TEXT, Fl_ALIGN_LEFT)
  Fl_Menu_AddImageLabel(bar, "File/Test2", "Test", "media/8x8.png", 0, nil, Fl_ALIGN_TEXT_OVER_IMAGE, Fl_ALIGN_RIGHT)
  
  Fl_Menu_AddImageLabel(bar, "File/Open1", "Open...", "media/16x16.png", 0, 0, Fl_ALIGN_IMAGE_NEXT_TO_TEXT, Fl_ALIGN_LEFT or FL_ALIGN_TOP)
  Fl_Menu_AddImageLabel(bar, "File/Open2", "Open...", "media/16x16.png", 0, 0, Fl_ALIGN_IMAGE_NEXT_TO_TEXT, Fl_ALIGN_CENTER)
  Fl_Menu_AddImageLabel(bar, "File/Open3", "Open...", "media/16x16.png", 0, 0, Fl_ALIGN_IMAGE_NEXT_TO_TEXT, Fl_ALIGN_RIGHT or FL_ALIGN_BOTTOM)
  
  Fl_Menu_AddImageLabel(bar, "File/Exit3", "Exit", "media/exit-2_32x32.png", 0, QuitCB, Fl_ALIGN_TEXT_NEXT_TO_IMAGE, Fl_ALIGN_RIGHT or FL_ALIGN_BOTTOM)
  Fl_Menu_AddImageLabel(bar, "File/Exit2", "Exit", "media/application-exit-4_32x32.png", 0, QuitCB, Fl_ALIGN_TEXT_NEXT_TO_IMAGE, Fl_ALIGN_CENTER)
  Fl_Menu_AddImageLabel(bar, "File/Exit1", "Exit", "media/exit-2_32x32.png", 0, QuitCB, Fl_ALIGN_TEXT_NEXT_TO_IMAGE, Fl_ALIGN_LEFT or FL_ALIGN_TOP)
  
  Fl_Run()
  
  Run

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• Araq (orginal) [2019-01-26T08:41:49+01:00] view original

  Please write nil. Sometimes programming is about working with the programming language rather than fighting it all the time. (Though fighting can be plenty of fun too.)

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