SEL和IMP類型的應用來源：UITableView-FDTemplateLayoutCell-master

- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    SEL selectors[] = {
        @selector(insertRow),
        @selector(insertSection),
        @selector(deleteSection)
    };
    if (buttonIndex < sizeof(selectors) / sizeof(SEL)) {
        //定義IMP類型，IMP類型就是實現(xiàn)方法
        void(*imp)(id, SEL) = (typeof(imp))[self methodForSelector:selectors[buttonIndex]];
        imp(self, selectors[buttonIndex]);
    }
}