list.go
func (l *List) Add(entries ...interface{}) {
	l.key.Lock()
	defer l.key.Unlock()
	l.underlyer = append(l.underlyer, entries...)
}
func (l *List) Add(entries ...interface{}) {
	l.key.Lock()
	defer l.key.Unlock()
	l.underlyer = append(l.underlyer, entries...)
}
// Add appends an entry to the logical end of the List.