On Sat, Mar 27, 2010 at 02:37:37AM +0800, PCMan wrote:
On Sat, Mar 27, 2010 at 12:17 AM, Julian Andres Klode <jak jak-linux org> wrote:Well, than f_finish() should probably not be there in the Volume interface; so I think that's a bug.So how can I fix this? Ship with a custom glib vapi file and remove *_finish from GVolume? Will this work? Or, can you make automatic generation of *_finish optional in Vala, or make the automatically generated *_finish override the abstract method in parent interface if its found?
For the second question, if I want to return a unowned GList, it has to be owned by the class and cannot be a local variable, right? Would you please add this to vala tutorial? I found it not documented and this behavior is not easy to figure out. In addition, this is not consistent with GObject with C. In C we can create a new GList and return it without the need to make it owned by anyone. The callee of the function is responsible to free the list.Because the list is unowned in can not be local, as it would go away once the function returns. If you want to return a locally created object, the return value can only be owned.This is quite different from C and C++ and is hard to understand for a C programmer I think.
No, it's not. The difference is just that instead of manually freeing the returned pointer, the return values are marked as unowned/owned, and Vala then adds code to free owned values automatically. In short, if you have to free a return value in C, it is owned; if you don't have to free it, it is unowned.
However, I don't get it. Let take GVolumeMonitor::get_volumes as example. It returns unowned GLib.List. So if I want to implement that, I should create a list and make it owned by the object instance and then return it unowned. However this is slightly different from the behavior of glib in C. In C GVolumeMonitor::get_volumes returns a "newly-allocated" GList containing a list of GObjects. The caller is responsible to g_list_foreach(list, g_object_unref, NULL); and then g_list_free(list);
So, the problem is that the function return values are falsely marked as unowned in the VAPI. I reported a bug for it at https://bugzilla.gnome.org/show_bug.cgi?id=614044
However, with Vala, how can I make vala methods return a "newly allocated GList" with all objects in it having increased ref_count? Automatic ref couting management in Vala is handy if you only use it in Vala but I find it difficult to make things right when interfacing with C code. I need to check the generated C code to see if it does what I really want. Any better guide for this? Already read Vala tutorial, but I still haven't get it.
Just don't mark the list as unowned. -- Julian Andres Klode - Debian Developer, Ubuntu Member See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/.
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