C++ wrapper classes for generated C API

[kevinthornberry]

Add option to generate C++ wrapper classes for use with the C API. These can be used if you intend to use the C API from another C++ environment, eg across an ABI boundary.

The wrapper classes are generated if the --c-wrapper-cpp-namespace CLI argument is provided - this is the namespace for the wrappers.

Example using --c-wrapper-cpp-namespace snap::test::c_wrappers :

my_module.djinni :

Size = record {
  width: i32;
  height: i32;
}

Window = interface +c {
  static create(): Window;
  show();
  hide();
  setSize(size: Size);
  setTitle(title: string);
}

Generated Size.h

// AUTOGENERATED FILE - DO NOT MODIFY!
// This file was generated by Djinni from test.djinni

#pragma once

#include "djinni/cpp/djinni_c.h"

#ifdef __cplusplus
extern "C" {
#endif // __cplusplus

typedef djinni_record_ref test_test_Size_ref;

test_test_Size_ref test_test_Size_new(int32_t width, int32_t height);

int32_t test_test_Size_get_width(test_test_Size_ref instance);
void test_test_Size_set_width(test_test_Size_ref instance, int32_t value);

int32_t test_test_Size_get_height(test_test_Size_ref instance);
void test_test_Size_set_height(test_test_Size_ref instance, int32_t value);

#ifdef __cplusplus
} // extern "C"
#endif // __cplusplus

#ifdef __cplusplus
#include <utility>
namespace snap::test::c_wrappers {

class Size {
public:

    Size(const test_test_Size_ref& ref) : _ref(ref) { djinni_ref_retain(_ref); }
    Size(test_test_Size_ref&& ref) noexcept : _ref(std::move(ref)) {}
    Size(const Size& other) : _ref(other._ref) { djinni_ref_retain(_ref); }
    Size(Size&& other) : _ref(std::move(other._ref)) { other._ref = nullptr; }
    ~Size() { djinni_ref_release(_ref); }
    Size& operator=(const Size& other) {
      if (&other != this) {
          auto old = _ref;
          _ref = other._ref;
          djinni_ref_retain(_ref);
          djinni_ref_release(old);
       }
       return *this;
    }
    Size& operator=(Size&& other) noexcept {
      if (&other != this) {
        auto old = _ref;
        _ref = other._ref;
        other._ref = nullptr;
    
        djinni_ref_release(old);
      }
      return *this;
    }
    Size& operator=(test_test_Size_ref&& ref) {
      auto old = _ref;
      _ref = ref;
      djinni_ref_release(old);
      return *this;
    }
    Size& operator=(const test_test_Size_ref& ref) {
      auto old = _ref;
      _ref = ref;
      djinni_ref_retain(ref);
      djinni_ref_release(old);
      return *this;
    }

    operator const test_test_Size_ref&() const { return _ref; }
    const test_test_Size_ref& _djinni_ref() const { return _ref; }

    int32_t width() const {
        return test_test_Size_get_width(_ref);
    }

    Size& width(int32_t value) {
        test_test_Size_set_width(_ref, value);
        return *this;
    }

    int32_t height() const {
        return test_test_Size_get_height(_ref);
    }

    Size& height(int32_t value) {
        test_test_Size_set_height(_ref, value);
        return *this;
    }

private:
    test_test_Size_ref _ref;
};

} // namespace snap::test::c_wrappers
#endif // __cplusplus

Generated Window.h :

// AUTOGENERATED FILE - DO NOT MODIFY!
// This file was generated by Djinni from test.djinni

#pragma once

#include "djinni/cpp/djinni_c.h"
#include "test/Size.h"
#include "test/Window.h"

#ifdef __cplusplus
extern "C" {
#endif // __cplusplus

typedef djinni_interface_ref test_test_Window_ref;

test_test_Window_ref test_test_Window_create();

void test_test_Window_show(test_test_Window_ref instance);

void test_test_Window_hide(test_test_Window_ref instance);

void test_test_Window_setSize(test_test_Window_ref instance, test_test_Size_ref size);

void test_test_Window_setTitle(test_test_Window_ref instance, djinni_string_ref title);

#ifdef __cplusplus
} // extern "C"
#endif // __cplusplus

#ifdef __cplusplus
#include <utility>
namespace snap::test::c_wrappers {

class Window {
public:

    Window(const test_test_Window_ref& ref) : _ref(ref) { djinni_ref_retain(_ref); }
    Window(test_test_Window_ref&& ref) noexcept : _ref(std::move(ref)) {}
    Window(const Window& other) : _ref(other._ref) { djinni_ref_retain(_ref); }
    Window(Window&& other) : _ref(std::move(other._ref)) { other._ref = nullptr; }
    ~Window() { djinni_ref_release(_ref); }
    Window& operator=(const Window& other) {
      if (&other != this) {
          auto old = _ref;
          _ref = other._ref;
          djinni_ref_retain(_ref);
          djinni_ref_release(old);
       }
       return *this;
    }
    Window& operator=(Window&& other) noexcept {
      if (&other != this) {
        auto old = _ref;
        _ref = other._ref;
        other._ref = nullptr;
    
        djinni_ref_release(old);
      }
      return *this;
    }
    Window& operator=(test_test_Window_ref&& ref) {
      auto old = _ref;
      _ref = ref;
      djinni_ref_release(old);
      return *this;
    }
    Window& operator=(const test_test_Window_ref& ref) {
      auto old = _ref;
      _ref = ref;
      djinni_ref_retain(ref);
      djinni_ref_release(old);
      return *this;
    }

    operator const test_test_Window_ref&() const { return _ref; }
    const test_test_Window_ref& _djinni_ref() const { return _ref; }

    static test_test_Window_ref create()  {
        return test_test_Window_create();
    }

    void show()  {
        test_test_Window_show(_ref);
    }

    void hide()  {
        test_test_Window_hide(_ref);
    }

    void setSize(test_test_Size_ref size)  {
        test_test_Window_setSize(_ref, size);
    }

    void setTitle(djinni_string_ref title)  {
        test_test_Window_setTitle(_ref, title);
    }

private:
    test_test_Window_ref _ref;
};

} // namespace snap::test::c_wrappers
#endif // __cplusplus

The wrappers can then be used to simplify C API usage:

#include "djinni/cpp/djinni_c_ref.hpp"

#include "my_module/Size.h"
#include "my_module/Window.h"

#include <stdio.h>

void testFunc() {
  using namespace snap::test::c_wrappers;

  Window win = Window::create();
  Size size = win.getSize();
  printf("size is %d x %d\n", size.width(), size.height());

  size.width(size.width() + 10);
  win.setSize(size);
  win.setTitle(djinni_string_new("foo", 3));
  win.show();
}

[kevinthornberry]

This file is better to review with whitespace ignored as there are some block indentation changes

[kevinthornberry]

Made this const ref to ensure correct constructor overload is called when doing things like

Ref<djinni_ref> myRef = ....
WrapperClass myWrapper(myRef.get());

The lvalue constructor should be used to ensure the ref count is appropriately incremented