gobject:object-property (object name &optional gtype)

object -- a g:object instance
name -- a string for the name of the property
gtype -- an optional g:type-t type ID for the property
value -- a value for the property

Gets or sets the property of an object. Setting and retrieving the gtk-application-prefer-dark-theme setting.

(defvar settings (gtk:settings-default))
=> SETTINGS
(setf (g:object-property settings "gtk-application-prefer-dark-theme") t)
=> T
(g:object-property settings "gtk-application-prefer-dark-theme")
=> T