Extension Points

Extension Points — Extension Points

Synopsis

#include <gio.h>

                    GIOExtension;
                    GIOExtensionPoint;
const char *        g_io_extension_get_name             (GIOExtension *extension);
gint                g_io_extension_get_priority         (GIOExtension *extension);
GType               g_io_extension_get_type             (GIOExtension *extension);
GIOExtension *      g_io_extension_point_get_extension_by_name
                                                        (GIOExtensionPoint *extension_point,
                                                         const char *name);
GList *             g_io_extension_point_get_extensions (GIOExtensionPoint *extension_point);
GType               g_io_extension_point_get_required_type
                                                        (GIOExtensionPoint *extension_point);
GIOExtension *      g_io_extension_point_implement      (const char *extension_point_name,
                                                         GType type,
                                                         const char *extension_name,
                                                         gint priority);
GIOExtensionPoint * g_io_extension_point_lookup         (const char *name);
GIOExtensionPoint * g_io_extension_point_register       (const char *name);
void                g_io_extension_point_set_required_type
                                                        (GIOExtensionPoint *extension_point,
                                                         GType type);
GTypeClass *         g_io_extension_ref_class           (GIOExtension *extension);

Description

GIOExtensionPoint provides a mechanism for modules to extend the functionality of the library or application that loaded it in an organized fashion.

An extension point is identified by a name, and it may optionally require that any implementation must by of a certain type (or derived thereof). Use g_io_extension_point_register() to register an extension point, and g_io_extension_point_set_required_type() to set a required type.

A module can implement an extension point by specifying the GType that implements the functionality. Additionally, each implementation of an extension point has a name, and a priority. Use g_io_extension_point_implement() to implement an extension point. 

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GIOExtensionPoint *ep;

/* Register an extension point */
ep = g_io_extension_point_register ("my-extension-point");
g_io_extension_point_set_required_type (ep, MY_TYPE_EXAMPLE);
 

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/* Implement an extension point */
G_DEFINE_TYPE (MyExampleImpl, my_example_impl, MY_TYPE_EXAMPLE);
g_io_extension_point_implement ("my-extension-point",
                                my_example_impl_get_type (),
                                "my-example",
                                10);

It is up to the code that registered the extension point how it uses the implementations that have been associated with it. Depending on the use case, it may use all implementations, or only the one with the highest priority, or pick a specific one by name.

To avoid opening all modules just to find out what extension points they implement, GIO makes use of a caching mechanism, see gio-querymodules. You are expected to run this command after installing a GIO module.

Details

GIOExtension

typedef struct _GIOExtension GIOExtension;

GIOExtensionPoint

typedef struct _GIOExtensionPoint GIOExtensionPoint;

g_io_extension_get_name ()

const char *        g_io_extension_get_name             (GIOExtension *extension);

Gets the name under which extension was registered.

Note that the same type may be registered as extension for multiple extension points, under different names.

extension :

 a GIOExtension

Returns :

 the name of extension.

g_io_extension_get_priority ()

gint                g_io_extension_get_priority         (GIOExtension *extension);

Gets the priority with which extension was registered.

extension :

 a GIOExtension

Returns :

 the priority of extension

g_io_extension_get_type ()

GType               g_io_extension_get_type             (GIOExtension *extension);

Gets the type associated with extension.

extension :

 a GIOExtension

Returns :

 the type of extension

g_io_extension_point_get_extension_by_name ()

GIOExtension *      g_io_extension_point_get_extension_by_name
                                                        (GIOExtensionPoint *extension_point,
                                                         const char *name);

Finds a GIOExtension for an extension point by name.

extension_point :

 a GIOExtensionPoint

name :

 the name of the extension to get

Returns :

 the GIOExtension for extension_point that has the given name, or NULL if there is no extension with that name. [transfer none]

g_io_extension_point_get_extensions ()

GList *             g_io_extension_point_get_extensions (GIOExtensionPoint *extension_point);

Gets a list of all extensions that implement this extension point. The list is sorted by priority, beginning with the highest priority.

extension_point :

 a GIOExtensionPoint

Returns :

 a GList of GIOExtensions. The list is owned by GIO and should not be modified. [element-type GIOExtension][transfer none]

g_io_extension_point_get_required_type ()

GType               g_io_extension_point_get_required_type
                                                        (GIOExtensionPoint *extension_point);

Gets the required type for extension_point.

extension_point :

 a GIOExtensionPoint

Returns :

 the GType that all implementations must have, or G_TYPE_INVALID if the extension point has no required type

g_io_extension_point_implement ()

GIOExtension *      g_io_extension_point_implement      (const char *extension_point_name,
                                                         GType type,
                                                         const char *extension_name,
                                                         gint priority);

Registers type as extension for the extension point with name extension_point_name.

If type has already been registered as an extension for this extension point, the existing GIOExtension object is returned.

extension_point_name :

 the name of the extension point

type :

 the GType to register as extension

extension_name :

 the name for the extension

priority :

 the priority for the extension

Returns :

 a GIOExtension object for GType

g_io_extension_point_lookup ()

GIOExtensionPoint * g_io_extension_point_lookup         (const char *name);

Looks up an existing extension point.

name :

 the name of the extension point

Returns :

 the GIOExtensionPoint, or NULL if there is no registered extension point with the given name

g_io_extension_point_register ()

GIOExtensionPoint * g_io_extension_point_register       (const char *name);

Registers an extension point.

name :

 The name of the extension point

Returns :

 the new GIOExtensionPoint. This object is owned by GIO and should not be freed

g_io_extension_point_set_required_type ()

void                g_io_extension_point_set_required_type
                                                        (GIOExtensionPoint *extension_point,
                                                         GType type);

Sets the required type for extension_point to type. All implementations must henceforth have this type.

extension_point :

 a GIOExtensionPoint

type :

 the GType to require

g_io_extension_ref_class ()

GTypeClass *         g_io_extension_ref_class           (GIOExtension *extension);

Gets a reference to the class for the type that is associated with extension.

extension :

 a GIOExtension

Returns :

 the GTypeClass for the type of extension. [transfer full]

See Also

Extending GIO
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