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GInitable

GInitable — Failable object initialization interface

Types and Values

Object Hierarchy

    GInterface
    ╰── GInitable

Prerequisites

GInitable requires GObject.

Known Derived Interfaces

GInitable is required by GNetworkMonitor.

Includes

#include <gio/gio.h>

Description

GInitable is implemented by objects that can fail during initialization. If an object implements this interface then it must be initialized as the first thing after construction, either via g_initable_init() or g_async_initable_init_async() (the latter is only available if it also implements GAsyncInitable).

If the object is not initialized, or initialization returns with an error, then all operations on the object except g_object_ref() and g_object_unref() are considered to be invalid, and have undefined behaviour. They will often fail with g_critical() or g_warning(), but this must not be relied on.

Users of objects implementing this are not intended to use the interface method directly, instead it will be used automatically in various ways. For C applications you generally just call g_initable_new() directly, or indirectly via a foo_thing_new() wrapper. This will call g_initable_init() under the cover, returning NULL and setting a GError on failure (at which point the instance is unreferenced).

For bindings in languages where the native constructor supports exceptions the binding could check for objects implemention GInitable during normal construction and automatically initialize them, throwing an exception on failure.

Functions

g_initable_init ()

gboolean
g_initable_init (GInitable *initable,
                 GCancellable *cancellable,
                 GError **error);

Initializes the object implementing the interface.

This method is intended for language bindings. If writing in C, g_initable_new() should typically be used instead.

The object must be initialized before any real use after initial construction, either with this function or g_async_initable_init_async().

Implementations may also support cancellation. If cancellable is not NULL, then initialization can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error G_IO_ERROR_CANCELLED will be returned. If cancellable is not NULL and the object doesn't support cancellable initialization the error G_IO_ERROR_NOT_SUPPORTED will be returned.

If the object is not initialized, or initialization returns with an error, then all operations on the object except g_object_ref() and g_object_unref() are considered to be invalid, and have undefined behaviour. See the introduction for more details.

Callers should not assume that a class which implements GInitable can be initialized multiple times, unless the class explicitly documents itself as supporting this. Generally, a class’ implementation of init() can assume (and assert) that it will only be called once. Previously, this documentation recommended all GInitable implementations should be idempotent; that recommendation was relaxed in GLib 2.54.

If a class explicitly supports being initialized multiple times, it is recommended that the method is idempotent: multiple calls with the same arguments should return the same results. Only the first call initializes the object; further calls return the result of the first call.

One reason why a class might need to support idempotent initialization is if it is designed to be used via the singleton pattern, with a GObjectClass.constructor that sometimes returns an existing instance. In this pattern, a caller would expect to be able to call g_initable_init() on the result of g_object_new(), regardless of whether it is in fact a new instance.

Parameters

initable

a GInitable.

 

cancellable

optional GCancellable object, NULL to ignore.

 

error

a GError location to store the error occurring, or NULL to ignore.

 

Returns

TRUE if successful. If an error has occurred, this function will return FALSE and set error appropriately if present.

Since: 2.22


g_initable_new ()

gpointer
g_initable_new (GType object_type,
                GCancellable *cancellable,
                GError **error,
                const gchar *first_property_name,
                ...);

Helper function for constructing GInitable object. This is similar to g_object_new() but also initializes the object and returns NULL, setting an error on failure.

Parameters

object_type

a GType supporting GInitable.

 

cancellable

optional GCancellable object, NULL to ignore.

 

error

a GError location to store the error occurring, or NULL to ignore.

 

first_property_name

the name of the first property, or NULL if no properties.

[nullable]

...

the value if the first property, followed by and other property value pairs, and ended by NULL.

 

Returns

a newly allocated GObject, or NULL on error.

[type GObject.Object][transfer full]

Since: 2.22


g_initable_new_valist ()

GObject *
g_initable_new_valist (GType object_type,
                       const gchar *first_property_name,
                       va_list var_args,
                       GCancellable *cancellable,
                       GError **error);

Helper function for constructing GInitable object. This is similar to g_object_new_valist() but also initializes the object and returns NULL, setting an error on failure.

Parameters

object_type

a GType supporting GInitable.

 

first_property_name

the name of the first property, followed by the value, and other property value pairs, and ended by NULL.

 

var_args

The var args list generated from first_property_name .

 

cancellable

optional GCancellable object, NULL to ignore.

 

error

a GError location to store the error occurring, or NULL to ignore.

 

Returns

a newly allocated GObject, or NULL on error.

[type GObject.Object][transfer full]

Since: 2.22


g_initable_newv ()

gpointer
g_initable_newv (GType object_type,
                 guint n_parameters,
                 GParameter *parameters,
                 GCancellable *cancellable,
                 GError **error);

g_initable_newv has been deprecated since version 2.54 and should not be used in newly-written code.

Use g_object_new_with_properties() and g_initable_init() instead. See GParameter for more information.

Helper function for constructing GInitable object. This is similar to g_object_newv() but also initializes the object and returns NULL, setting an error on failure.

Parameters

object_type

a GType supporting GInitable.

 

n_parameters

the number of parameters in parameters

 

parameters

the parameters to use to construct the object.

[array length=n_parameters]

cancellable

optional GCancellable object, NULL to ignore.

 

error

a GError location to store the error occurring, or NULL to ignore.

 

Returns

a newly allocated GObject, or NULL on error.

[type GObject.Object][transfer full]

Since: 2.22

Types and Values

GInitable

typedef struct _GInitable GInitable;

Interface for initializable objects.

Since: 2.22


struct GInitableIface

struct GInitableIface {
  GTypeInterface g_iface;

  /* Virtual Table */

  gboolean    (* init) (GInitable    *initable,
			GCancellable *cancellable,
			GError      **error);
};

Provides an interface for initializing object such that initialization may fail.

Members

init ()

Initializes the object.

 

Since: 2.22

See Also

GAsyncInitable

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