GObject Reference Manual: GTypeModule

## GTypeModule GTypeModule — Type loading modules |

## Synopsis

    #include <glib-object.h>

    struct              GTypeModule;
    struct              GTypeModuleClass;
    gboolean            g_type_module_use                   (GTypeModule *module);
    void                g_type_module_unuse                 (GTypeModule *module);
    void                g_type_module_set_name              (GTypeModule *module,
                                                             const gchar *name);
    GType               g_type_module_register_type         (GTypeModule *module,
                                                             GType parent_type,
                                                             const gchar *type_name,
                                                             const GTypeInfo *type_info,
                                                             GTypeFlags flags);
    void                g_type_module_add_interface         (GTypeModule *module,
                                                             GType instance_type,
                                                             GType interface_type,
                                                             const GInterfaceInfo *interface_info);
    GType               g_type_module_register_enum         (GTypeModule *module,
                                                             const gchar *name,
                                                             const GEnumValue *const_static_values);
    GType               g_type_module_register_flags        (GTypeModule *module,
                                                             const gchar *name,
                                                             const GFlagsValue *const_static_values);
    #define             G_DEFINE_DYNAMIC_TYPE               (TN,
                                                             t_n,
                                                             T_P)
    #define             G_DEFINE_DYNAMIC_TYPE_EXTENDED      (TypeName,
                                                             type_name,
                                                             TYPE_PARENT,
                                                             flags,
                                                             CODE)
    #define             G_IMPLEMENT_INTERFACE_DYNAMIC       (TYPE_IFACE,
                                                             iface_init)

## Object Hierarchy

      GObject
       +----GTypeModule

## Implemented Interfaces

GTypeModule implements GTypePlugin.

## Description

GTypeModule provides a simple implementation of the GTypePlugin interface. The model of GTypeModule is a dynamically loaded module which implements some number of types and interface implementations. When the module is loaded, it registers its types and interfaces using `g_type_module_register_type()` and `g_type_module_add_interface()`. As long as any instances of these types and interface implementations are in use, the module is kept loaded. When the types and interfaces are gone, the module may be unloaded. If the types and interfaces become used again, the module will be reloaded. Note that the last unref cannot happen in module code, since that would lead to the caller's code being unloaded before `g_object_unref()` returns to it.

Keeping track of whether the module should be loaded or not is done by using a use count - it starts at zero, and whenever it is greater than zero, the module is loaded. The use count is maintained internally by the type system, but also can be explicitly controlled by `g_type_module_use()` and `g_type_module_unuse()`. Typically, when loading a module for the first type, `g_type_module_use()` will be used to load it so that it can initialize its types. At some later point, when the module no longer needs to be loaded except for the type implementations it contains, `g_type_module_unuse()` is called.

GTypeModule does not actually provide any implementation of module loading and unloading. To create a particular module type you must derive from GTypeModule and implement the load and unload functions in GTypeModuleClass.

## Details

### struct GTypeModule

    struct GTypeModule {
      gchar *name;
    };

The members of the GTypeModule structure should not be accessed directly, except for the `name` field.

gchar *`name`; | the name of the module

### struct GTypeModuleClass

    struct GTypeModuleClass {
      GObjectClass parent_class;

      gboolean (* load)   (GTypeModule *module);
      void     (* unload) (GTypeModule *module);
    };

In order to implement dynamic loading of types based on GTypeModule, the `load` and `unload` functions in GTypeModuleClass must be implemented.

GObjectClass `parent_class`; | the parent class
`load` () | loads the module and registers one or more types using `g_type_module_register_type()`.
`unload` () | unloads the module

### g_type_module_use ()

    gboolean            g_type_module_use                   (GTypeModule *module);

Increases the use count of a GTypeModule by one. If the use count was zero before, the plugin will be loaded. If loading the plugin fails, the use count is reset to its prior value.

`module` : | a GTypeModule
Returns : | `FALSE` if the plugin needed to be loaded and loading the plugin failed.

### g_type_module_unuse ()

    void                g_type_module_unuse                 (GTypeModule *module);

Decreases the use count of a GTypeModule by one. If the result is zero, the module will be unloaded. (However, the GTypeModule will not be freed, and types associated with the GTypeModule are not unregistered. Once a GTypeModule is initialized, it must exist forever.)

`module` : | a GTypeModule

### g_type_module_set_name ()

    void                g_type_module_set_name              (GTypeModule *module,
                                                             const gchar *name);

Sets the name for a GTypeModule

`module` : | a GTypeModule.
`name` : | a human-readable name to use in error messages.

### g_type_module_register_type ()

    GType               g_type_module_register_type         (GTypeModule *module,
                                                             GType parent_type,
                                                             const gchar *type_name,
                                                             const GTypeInfo *type_info,
                                                             GTypeFlags flags);

Looks up or registers a type that is implemented with a particular type plugin. If a type with name `type_name` was previously registered, the GType identifier for the type is returned, otherwise the type is newly registered, and the resulting GType identifier returned.

When reregistering a type (typically because a module is unloaded then reloaded, and reinitialized), `module` and `parent_type` must be the same as they were previously.

As long as any instances of the type exist, the type plugin will not be unloaded.

`module` : | a GTypeModule
`parent_type` : | the type for the parent class
`type_name` : | name for the type
`type_info` : | type information structure
`flags` : | flags field providing details about the type
Returns : | the new or existing type ID

### g_type_module_add_interface ()

    void                g_type_module_add_interface         (GTypeModule *module,
                                                             GType instance_type,
                                                             GType interface_type,
                                                             const GInterfaceInfo *interface_info);

Registers an additional interface for a type, whose interface lives in the given type plugin. If the interface was already registered for the type in this plugin, nothing will be done.

As long as any instances of the type exist, the type plugin will not be unloaded.

`module` : | a GTypeModule
`instance_type` : | type to which to add the interface.
`interface_type` : | interface type to add
`interface_info` : | type information structure

### g_type_module_register_enum ()

    GType               g_type_module_register_enum         (GTypeModule *module,
                                                             const gchar *name,
                                                             const GEnumValue *const_static_values);

Looks up or registers an enumeration that is implemented with a particular type plugin. If a type with name `type_name` was previously registered, the GType identifier for the type is returned, otherwise the type is newly registered, and the resulting GType identifier returned.

As long as any instances of the type exist, the type plugin will not be unloaded.

`module` : | a GTypeModule
`name` : | name for the type
`const_static_values` : | an array of GEnumValue structs for the possible enumeration values. The array is terminated by a struct with all members being 0.
Returns : | the new or existing type ID

Since 2.6

### g_type_module_register_flags ()

    GType               g_type_module_register_flags        (GTypeModule *module,
                                                             const gchar *name,
                                                             const GFlagsValue *const_static_values);

Looks up or registers a flags type that is implemented with a particular type plugin. If a type with name `type_name` was previously registered, the GType identifier for the type is returned, otherwise the type is newly registered, and the resulting GType identifier returned.

As long as any instances of the type exist, the type plugin will not be unloaded.

`module` : | a GTypeModule
`name` : | name for the type
`const_static_values` : | an array of GFlagsValue structs for the possible flags values. The array is terminated by a struct with all members being 0.
Returns : | the new or existing type ID

Since 2.6

### G_DEFINE_DYNAMIC_TYPE()

    #define G_DEFINE_DYNAMIC_TYPE(TN, t_n, T_P)          G_DEFINE_DYNAMIC_TYPE_EXTENDED (TN, t_n, T_P, 0, {})

A convenience macro for dynamic type implementations, which declares a class initialization function, an instance initialization function (see GTypeInfo for information about these) and a static variable named `t_n`_parent_class pointing to the parent class. Furthermore, it defines a `*_get_type()` and a static `*_register_type()` function for use in your ``module_init()``. See `G_DEFINE_DYNAMIC_TYPE_EXTENDED()` for an example.

`TN` : | The name of the new type, in Camel case.
`t_n` : | The name of the new type, in lowercase, with words separated by '_'.
`T_P` : | The GType of the parent type.

Since 2.14

### G_DEFINE_DYNAMIC_TYPE_EXTENDED()

    #define             G_DEFINE_DYNAMIC_TYPE_EXTENDED(TypeName, type_name, TYPE_PARENT, flags, CODE)

A more general version of `G_DEFINE_DYNAMIC_TYPE()` which allows to specify GTypeFlags and custom code.

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    G_DEFINE_DYNAMIC_TYPE_EXTENDED (GtkGadget,
                                    gtk_gadget,
                                    GTK_TYPE_THING,
                                    0,
                                    G_IMPLEMENT_INTERFACE_DYNAMIC (TYPE_GIZMO,
                                                                   gtk_gadget_gizmo_init));

expands to

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    static void     gtk_gadget_init              (GtkGadget      *self);
    static void     gtk_gadget_class_init        (GtkGadgetClass *klass);
    static void     gtk_gadget_class_finalize    (GtkGadgetClass *klass);

    static gpointer gtk_gadget_parent_class = NULL;
    static GType    gtk_gadget_type_id = 0;

    static void     gtk_gadget_class_intern_init (gpointer klass)
    {
      gtk_gadget_parent_class = g_type_class_peek_parent (klass);
      gtk_gadget_class_init ((GtkGadgetClass*) klass);
    }

    GType
    gtk_gadget_get_type (void)
    {
      return gtk_gadget_type_id;
    }

    static void
    gtk_gadget_register_type (GTypeModule *type_module)
    {
      const GTypeInfo g_define_type_info = {
        sizeof (GtkGadgetClass),
        (GBaseInitFunc) NULL,
        (GBaseFinalizeFunc) NULL,
        (GClassInitFunc) gtk_gadget_class_intern_init,
        (GClassFinalizeFunc) gtk_gadget_class_finalize,
        NULL,   // class_data
        sizeof (GtkGadget),
        0,      // n_preallocs
        (GInstanceInitFunc) gtk_gadget_init,
        NULL    // value_table
      };
      gtk_gadget_type_id = g_type_module_register_type (type_module,
                                                        GTK_TYPE_THING,
                                                        "GtkGadget",
                                                        &g_define_type_info,
                                                        (GTypeFlags) flags);
      {
        const GInterfaceInfo g_implement_interface_info = {
          (GInterfaceInitFunc) gtk_gadget_gizmo_init
        };
        g_type_module_add_interface (type_module, g_define_type_id, TYPE_GIZMO, &g_implement_interface_info);
      }
    }

`TypeName` : | The name of the new type, in Camel case.
`type_name` : | The name of the new type, in lowercase, with words separated by '_'.
`TYPE_PARENT` : | The GType of the parent type.
`flags` : | GTypeFlags to pass to `g_type_module_register_type()`
`CODE` : | Custom code that gets inserted in the *_get_type() function.

Since 2.14

### G_IMPLEMENT_INTERFACE_DYNAMIC()

    #define             G_IMPLEMENT_INTERFACE_DYNAMIC(TYPE_IFACE, iface_init)

A convenience macro to ease interface addition in the `_C_` section of `G_DEFINE_DYNAMIC_TYPE_EXTENDED()`. See `G_DEFINE_DYNAMIC_TYPE_EXTENDED()` for an example.

Note that this macro can only be used together with the G_DEFINE_DYNAMIC_TYPE_EXTENDED macros, since it depends on variable names from that macro.

`TYPE_IFACE` : | The GType of the interface to add
`iface_init` : | The interface init function

Since 2.24

## See Also

GTypePlugin | The abstract type loader interface.
GModule | Portable mechanism for dynamically loaded modules.