removeFirst method
T?
removeFirst()
Removes and returns the first node data from this list. This method returns null if the list is empty.
Implementation
T? removeFirst() {
if (_head == null) return null;
T? removedData = _head!.data;
if (_head == _tail) {
_head = _tail = null;
} else {
_head = _head!.next;
}
_size--;
return removedData;
}