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use super::DoublyLinkedList;
impl<T> DoublyLinkedList<T> {
/// Retrieves a reference to the first element in the `DoublyLinkedList`, if it exists.
///
/// # Returns
///
/// - `Some(&mut T)`: A mutable reference to the first element in the list.
/// - `None`: If the list is empty.
///
/// # Examples
///
/// ```
/// use villa01_data_structures::doubly_linked_list::DoublyLinkedList;
///
/// let mut list = DoublyLinkedList::new();
/// assert_eq!(list.get_first_mut(), None);
///
/// list.insert_at_beginning(42);
/// list.insert_at_beginning(84);
///
/// assert_eq!(list.get_first_mut(), Some(&mut 84));
/// ```
/// # Complexity
/// - `O(1)`
///
pub fn get_first_mut(&self) -> Option<&mut T> {
match self.head {
Some(head) => unsafe { return Some(&mut (*head).data) },
None => None,
}
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_get_first_empty_list() {
let list: DoublyLinkedList<usize> = DoublyLinkedList::new();
let i = list.get_first_mut();
assert!(i.is_none());
}
#[test]
fn test_get_first() {
let value = 10;
let list: DoublyLinkedList<usize> = DoublyLinkedList::with_value(value);
let i = list.get_first_mut();
assert!(i.is_some());
let ivalue = i.unwrap();
assert_eq!(value, *(ivalue));
(*ivalue) += 1;
let new_value = list.get_first().unwrap();
assert_eq!(value + 1, *(new_value));
}
}