Initializes the object implementing the interface. 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 ??? section introduction for more details. Implementations of this method must be idempotent, i.e. multiple calls to this function with the same argument should return the same results. Only the first call initializes the object, further calls return the result of the first call. This is so that it's safe to implement the singleton pattern in the GObject constructor function. Since 2.22
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. Since 2.22
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. Since 2.22
the main Gtk struct
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.