Registering an enum type in GLib’s type system
##############################################

:date: 2013-01-06T02:34:03Z
:category: blog
:tags: c,development,glib
:url: blog/2013/1/6/registering-an-enum-type-in-glib-s-type-system.html
:save_as: blog/2013/1/6/registering-an-enum-type-in-glib-s-type-system.html
:status: published
:author: Gergely Polonkai

I faced a problem in my `GLib <https://developer.gnome.org/glib/>`_ self-teaching project, `wMUD
<https://github.com/gergelypolonkai/wmud>`_ today.  I wanted to register a signal for a
``GObject``, whose handler should accept two ``enum`` parameters for which I had to register a new
``GEnum`` type in the ``GObject`` type system.  However, the `documentation on this feature
<https://developer.gnome.org/gobject/unstable/gtype-non-instantiable.html>`_ (thanks for pointing
out goes to `hashem` on ``#gnome-hackers``) is not… uhm…  obvious.  Making the long story short, I
have checked with the ``GIO`` sources for an example, and using that, I have created this small,
working chunk:

.. code-block:: c

   #ifndef __WMUD_CLIENT_STATE_H__
   #define __WMUD_CLIENT_STATE_H__

   #include <glib-object.h>

   /**
    * WmudClientState:
    * @WMUD_CLIENT_STATE_FRESH: Client is newly connected. Waiting for a login
    *     player name
    * @WMUD_CLIENT_STATE_PASSWAIT: Login player name is entered, waiting for a
    *     login password
    * @WMUD_CLIENT_STATE_MENU: Authentication was successful, player is now in the
    *     main game menu
    * @WMUD_CLIENT_STATE_INGAME: Character login was successful, player is now
    *     in-game
    * @WMUD_CLIENT_STATE_YESNO: Player was asked a yes/no question, and we are
    *     waiting for the answer. client.yesNoCallback MUST be set at this point!
    *     TODO: if wmudClient had a prevState field, and there would be some hooks
    *     that are called before and after the client enters a new state, this
    *     could be a three-state stuff, in which the player can enter e.g ? as
    *     the answer, so they would be presented with the question again.
    * @WMUD_CLIENT_STATE_REGISTERING: Registering a new player. Waiting for the
    *     e-mail address to be given
    * @WMUD_CLIENT_STATE_REGEMAIL_CONFIRM: E-mail address entered séms valid,
    *     waiting for confirmation
    *
    * Game client states.
    */
   typedef enum {
           WMUD_CLIENT_STATE_FRESH,
           WMUD_CLIENT_STATE_PASSWAIT,
           WMUD_CLIENT_STATE_MENU,
           WMUD_CLIENT_STATE_INGAME,
           WMUD_CLIENT_STATE_YESNO,
           WMUD_CLIENT_STATE_REGISTERING,
           WMUD_CLIENT_STATE_REGEMAIL_CONFIRM
   } WmudClientState;


   GType wmud_client_state_get_type (void) G_GNUC_CONST;
   #define WMUD_TYPE_CLIENT_STATE (wmud_client_state_get_type())

   #endif /* __WMUD_CLIENT_STATE_H__ */

.. code-block:: c

   #include "wmudclientstate.h"

   GType
   wmud_client_state_get_type (void)
   {
           static volatile gsize g_define_type_id__volatile = 0;

           if (g_once_init_enter(&g_define_type_id__volatile)) {
                   static const GEnumValue values[] = {
                           { WMUD_CLIENT_STATE_FRESH,            "WMUD_CLIENT_STATE_FRESH",            "fresh"            },
                           { WMUD_CLIENT_STATE_PASSWAIT,         "WMUD_CLIENT_STATE_PASSWAIT",         "passwait"         },
                           { WMUD_CLIENT_STATE_MENU,             "WMUD_CLIENT_STATE_MENU",             "menu"             },
                           { WMUD_CLIENT_STATE_INGAME,           "WMUD_CLIENT_STATE_INGAME",           "ingame"           },
                           { WMUD_CLIENT_STATE_YESNO,            "WMUD_CLIENT_STATE_YESNO",            "yesno"            },
                           { WMUD_CLIENT_STATE_REGISTERING,      "WMUD_CLIENT_STATE_REGISTERING",      "registering"      },
                           { WMUD_CLIENT_STATE_REGEMAIL_CONFIRM, "WMUD_CLIENT_STATE_REGEMAIL_CONFIRM", "regemail-confirm" },
                           { 0,                                  NULL,                                 NULL }
                   };
                   GType g_define_type_id = g_enum_register_static(g_intern_static_string("WmudClientState"), values);
                   g_once_init_leave(&g_define_type_id__volatile, g_define_type_id);
           }

           return g_define_type_id__volatile;
   }

Still, it can be made more perfect by using the `glib-mkenums
<http://developer.gnome.org/gobject/stable/glib-mkenums.html>`_ tool.  I will read through the
GLib Makefiles tomorrow for some hints on this.

Edit: you can find the glib-mkenums solution `here
<{filename}2014-08-16-registering-an-enum-type-in-glib-glib-mkenums-magic.rst>`_.