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

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+---
+layout:    post
+title:     "Emacs: Implement a GObject’s virtual function"
+date:      2016-01-13 15:31:12+02:00
+tags:      [c, development, emacs]
+published: true
+author:
+  name: "Gergely Polonkai"
+  email: "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 gergelypolonkai/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`.