GooCanvas items constructors don't follow GObject conventions

[Éric ALBER <eric alber gmail com>]

Hello,

I'm developing a small project using vala. I use GooCanvas through the bindings provided by vala.
I have an annoying problem with GooCanvas item creation methods. For example with GooCanvasRect:



If I want to create an instance of the object, I use

    GooCanvasItem* item = goo_canvas_rect_new(parent_item, 10, 10, 100, 100);

Now I have a sort of weak reference on the item, I mean I don't need to call g_object_unref(item) as parent_item is the owner of this new instance.


But if I create a new instance with these parameters:

    GooCanvasItem* item = goo_canvas_rect_new(NULL, 10, 10, 100, 100);

Here I have a strong reference on the item, I need to call g_object_unref(item) to be sure the object is freed.


This means that the ownership of the created instance depends on the parameters given to the method. This makes the method unwrappable in vala as vala expects the return value of a function to be either weak or strong but not dependent on the parameters of the function. More specifically, constructors are expected to return strong references. In the current state, we cannot subclass any item with the vala bindings due to that problem.


Moreover, In GObject based libraries (GDK, GTK+, etc..), the my_object_new(int param1, int param2) methods are just shortcuts to:

    g_object_new(MY_TYPE_OBJECT, "param1", param1, "param2", param2, NULL);

All specific initialization should take place in a "construct" method, not in the my_object_new mehtod.


So I tried, the following code which should be the same than the examples given above:


    GooCanvasItem* item = g_object_new(GOO_TYPE_CANVAS_RECT, "parent", parent_item, "x", 10.0, "y", 10.0, "width", 100.0, "height", 100.0, NULL);
    
Here I get an instance which properties are initialized with the same values than in the first example, but I have a strong reference on it, I always have to call g_object_unref on it whether parent_item is NULL or not. If parent_item != NULL, ref_count == 2

If this was the implementation of goo_canvas_rect_new, the method could be bound properly in vala.
I'm willing to help and propose a patch to fix the problem, but I would like to know what is your preferred fix:

1) Fix goo_canvas_*_new() methods.
- Pros: API is now clean and similar to all other GObject based libraries
- Cons: All programs/bindings using GooCanvas need to call g_object_unref() after creating an instance. Non fixed programs will leak memory

Maybe the version number should be increased to make the API change clear to everybody.

2) Add another constructor method with a different name like goo_canvas_*_new_ref() or goo_canvas_*_create() (which one do you prefer?)


- Pros: All programs using GooCanvas continue to work normally

- Cons: API is a bit different than other GObject based libraries


Tell me what you think about that.

Best Regards,

Eric