void GCompletionFieldSetCompletion(GGadget *g,GTextCompletionHandler completion) {
    ((GCompletionField *) g)->completion = completion;
    ((GTextField *) g)->accepts_tabs = ((GCompletionField *) g)->completion != NULL;
}
void GCompletionFieldSetCompletion(GGadget *g,GTextCompletionHandler completion) {
    ((GCompletionField *) g)->completion = completion;
    ((GTextField *) g)->accepts_tabs = ((GCompletionField *) g)->completion != NULL;
}