func (l *List) Swap(x, y uint) bool {
	l.key.Lock()
	defer l.key.Unlock()
	return l.swap(x, y)
}
func (l *List) Swap(x, y uint) bool {
	l.key.Lock()
	defer l.key.Unlock()
	return l.swap(x, y)
}
func ( l * List ) Swap ( x , y uint ) bool { l . key . Lock ( ) defer l . key . Unlock ( ) return l . swap ( x , y ) }
// Swap switches the values that are stored at positions `x` and `y`
Swap switches the values that are stored at positions x and y