gergelypolonkai-web-jekyll/_posts/2016-01-13-emacs-implement-a-gobject-s-virtual-function.md

layout	title	date	tags	published	author
post	Emacs: Implement a GObject’s virtual function	2016-01-13 13:31:12	c development emacs	true	name email Gergely Polonkai gergely@polonkai.eu

I have recently started creating a GLib implementation of the Matrix.org API. For that, I have created a GObject interface, MatrixAPI, which has as many virtual functions as API calls (which is a lot, and expanding). This way I ended up with the following scenario.

In matrix-api.h I had a struct like this, with a lot more elements:

typedef struct {
    void (*initial_sync)(MatrixAPI *api,
                         MatrixAPICallback callback,
                         gpointer user_data,
                         GError **error);
    void (*sync)(MatrixAPI *api,
                 MatrixAPICallback callback,
                 gpointer user_data,
                 GError **error);
    …

And in matrix-http-api.c, which implements MatrixAPI, I have a function like this (again, with a lot more elements):

static void
matrix_http_api_matrix_api_init(GObjectInterface *iface)
{
    iface->initial_sync = i_initial_sync;
    iface->sync = i_sync;
    …
}

And every time I wanted to implement a new function from the vtable, I had to copy the prototype, and add an iface->foo_bar = i_foo_bar line and an actual function header for i_foo_bar with the same parameters. That’s a cumbersome job for more than 40 function headers. But emacs comes to the rescue!

{% gist bfd36be8b515edced3d2 implement-gobject-vfunc.el %}

Now all I have to do is to copy the whole vtable entry into matrix_http_api_matrix_api_init(), execute M-x implement-gobject-vfunc, then put the same vtable entry somewhere before the interface init function, and execute M-x implement-gobject-vfunc-prototype.