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4229 :: creating code for C++ class

• adrianv (orginal) [2018-09-24T14:48:21+02:00] view original

  Hi, I try to subclass a C++ class in nim and implement some features in nim. Here is what I do:

  {.emit:"""
  
  class Foo {
  public:
    int data;
    Foo() {}
  };
  
  class Bar: public Foo {
  public:
    int d2;
    Bar() : Foo() {}
    ~Bar();
  
  };
  
  """.}
  
  {.deadCodeElim: off.} # seems no to work
  
  type
    Foo* {.importcpp: "Foo", inheritable.} = object
      data: cint
    Bar* {.importcpp: "Bar".} = object of Foo
      d2: cint
  
  proc newBar(): ptr Bar {.importcpp:"new Bar()".}
  
  proc cdelete*[T](x: ptr T) {.importcpp: "delete #", nodecl.}
  
  proc killBar() {.codegenDecl: "Bar::~Bar$3", used, exportc.} =
    var self {.noInit.}: ptr Bar
    {.emit: "self = this;".}
    echo "kill it ", self.d2
  
  proc main() =
    var f: Foo
    var b = newBar()
    b.d2 = 12
    cdelete b
  
  main()
  
  Run

  the code actual compiles and runs, but there are some things I don't like:

  1. killBar is not in the .cpp file unless I use the pragma exportc - this is not a solution for me because exportc together with --header also writes the declaration of killBar = Bar::~Bar() into the header file which produces an invalid header file. {.deadCodeElim: off.} seems to have no effect here. exportc was the only solution I found to keep killBar. It would be nice, if we could have a pragma on a per proc base to keep a proc from being eliminated.
  2. the assignment from "this" to "self" is also very hacky because it it could trigger a hidden copy. I tried:

  proc killBar() {.codegenDecl: "Bar::~Bar$3", used, exportc.} =
    var self {.importcpp: "this", nodecl, noInit.}: ptr Bar
    #{.emit: "self = this;".}
    echo "kill it ", self.d2
  
  Run

  but this still produces a line with

  Bar* this;
  Run

  into the C++ code. the nodecl seems to be ignored here.

  Has anybody some hints how to improve that ?

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