// https://developer.gnome.org/gobject/stable/gtype-conventions.html

boilerplate-window.h:
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#define BOILERPLATE_TYPE_WINDOW_STATE (boilerplate_window_state_get_type ())

G_DECLARE_FINAL_TYPE (BoilerplateWindowState, boilerplate_window_state, BOILERPLATE, WINDOW_STATE, GObject)

typedef struct {
    GObject parent_instance;

    int width;
    int height;
    int x;
    int y;
    gboolean maximized;
    gboolean fullscreen;
} BoilerplateWindowState;

struct _BoilerplateWindow {
    GtkApplicationWindow parent_instance;

    BoilerplateWindowState *state;
};


boilerplate-window.c:
static void boilerplate_window_constructed ():
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self->state = g_object_new (boilerplate_window_state_get_type (), NULL);



boilerplate-window.c:
static void boilerplate_window_constructed ():
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static gboolean boilerplate_window_window_state_event ():
    gboolean maximized;
    gboolean fullscreen;



general files:
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g_return_if_fail (BOILERPLATE_IS_APPLICATION (obj));
g_return_if_fail (BOILERPLATE_IS_WINDOW (obj));
g_return_if_fail (BOILERPLATE_IS_WINDOW_STATE (obj));
g_return_if_fail (BOILERPLATE_IS_LOG (obj));


g_assert (BOILERPLATE_IS_APPLICATION (obj));
g_assert (BOILERPLATE_IS_WINDOW (obj));
g_assert (BOILERPLATE_IS_WINDOW_STATE (obj));
g_assert (BOILERPLATE_IS_LOG (obj));