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1705 :: C wrapper var parameter problem

• Stefan_Salewski (orginal) [2015-10-12T19:20:39+02:00] view original

  ExampleAppPrefsPrivate = ptr ExampleAppPrefsPrivateObj
  ExampleAppPrefsPrivateObj = object
    settings: gio.GSettings
    font: gtk3.Widget
    transition: gtk3.Widget
  
  proc clear_object*(object_ptr: ptr GObject) {.importc: "g_clear_object", libgobj.}
  proc varclear_object*(object_ptr: var GObject) {.importc: "g_clear_object", libgobj.}
  
  # clear_object(cast[ptr GObject]( addr priv.settings))
  varclear_object(priv.settings)
  
  assert(priv.settings == nil)
  Run

  My assumption was, that the variant with var parameter would work the same as that one with the explicit pointer. But for the proc with var parameter assert fails, so library function manages not to set it to nil. I guess the problem is that I have not a plain parameter, but a field in a Nim object. Is that not allowed?

  Maybe I should mention that the parameter is defined with volatile in C lib, I do not know if the makes a difference:

  void g_clear_object (volatile GObject **object_ptr);

  [EDIT]

  For the ptr version I have this C code:

  Dl_143734(((Gobjectobj143085**) (&(*priv).settings)));
   nimln(45, "exampleappprefs.nim");
   {
           if (!!(((*priv).settings == NIM_NIL))) goto LA4;
           failedassertimpl_88591(((NimStringDesc*) &TMP609));
   }

  And for var version:

  Gobjectobj143085** LOC2;
  LOC2 = 0;
  LOC2 = &(*priv).settings->Sup;
  Dl_143741((&LOC2));
  nimln(46, "exampleappprefs.nim");
  {
          if (!!(((*priv).settings == NIM_NIL))) goto LA5;
          failedassertimpl_88591(((NimStringDesc*) &TMP609));
  }

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• Araq (orginal) [2015-10-13T00:46:11+02:00] view original

  Well both versions seem to be wrong since a GObject **p is a p: ptr ptr GObject or a p: var ptr GObject in Nim. It's bad luck that it works for one variant and not for the other. I don't think the volatile means anything here.

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• Stefan_Salewski (orginal) [2015-10-13T12:23:40+02:00] view original

  OK, one has to know that in our new notation without T/P prefix

  GObject* =  ptr GObjectObj
  GObjectPtr* = ptr GObjectObj
  GObjectObj* = object of GTypeInstanceObj

  So you think that a var parameter should work in this notation? Then I think I should make a github bugtracker report? Unfortunately this example compiles only with latest wrapper set for GTK 3.18, which is not fully finished. I will see if I can make an example without GTK.

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• Araq (orginal) [2015-10-13T13:28:40+02:00] view original

  Sure, please go ahead and report it. Surely there is a bug somewhere.

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• Stefan_Salewski (orginal) [2015-10-13T22:46:50+02:00] view original

  Is this example good enough?

  type
    Base = ptr BaseObj
    BaseObj = object of Rootobj
      b: int
    
    Dia = ptr DiaObj
    DiaObj = object of BaseObj
      i: int
    
    GSettings = ptr GSettingsObj
    GSettingsObj = object of BaseObj
      j: int
    
    ExampleAppPrefs* = ptr ExampleAppPrefsObj
    ExampleAppPrefsObj = object of DiaObj
    
    ExampleAppPrefsClass = ptr ExampleAppPrefsClassObj
    ExampleAppPrefsClassObj = object of DiaObj
      p: ExampleAppPrefsPrivate
    
    ExampleAppPrefsPrivate = ptr ExampleAppPrefsPrivateObj
    ExampleAppPrefsPrivateObj = object
      settings: GSettings
  
  var
    eapco: ExampleAppPrefsClassObj
    dobj: DiaObj
    gso: GSettingsObj
    eappo: ExampleAppPrefsPrivateObj
    
    eapc: ExampleAppPrefsClass
    gs: GSettings
    eapp: ExampleAppPrefsPrivate
  
  eapc = addr eapco
  eapc.p = addr eappo
  eappo.settings = addr gso
  
  proc xvarclear_object(object_ptr: var Base) =
   object_ptr = nil
  
  proc example_app_prefs_dispose(obj: ExampleAppPrefsClass) {.cdecl.} =
    var priv: ExampleAppPrefsPrivate
    priv = ExampleAppPrefsClass(obj).p
    echo "yyyyyyyyyyyyyyyyyy"
    xvarclear_object(priv.settings)
    assert(priv.settings == nil)
    echo "xxxxxxxxxxxxxx"
  
  example_app_prefs_dispose(eapc)
  Run

  nim c b.nim
  $ ./b
  yyyyyyyyyyyyyyyyyy
  Traceback (most recent call last)
  b.nim(50)                b
  b.nim(47)                example_app_prefs_dispose
  system.nim(3224)         failedAssertImpl
  system.nim(3216)         raiseAssert
  system.nim(2425)         sysFatal
  Error: unhandled exception: priv.settings == nil  [AssertionError]
  stefan@AMD64X2 ~/nab $ nim -v
  Nim Compiler Version 0.11.3 (2015-08-11) [Linux: amd64]

  This is my third attempt, of course it is very ugly, but from my current understanding it shows that problem. The first two attemps, written from scratch worked fine. So maybe something is special for this example, or maybe I am doing something really wrong.

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