List::pop_front

pub fn pop_front() -> Option<T>

use collections::list::{List};

Removes and returns the front value, or None when the list is empty. Constant time.

Called on a List value as value.pop_front(…).

Returns#

Option<T>

Contracts#

Checked according to --contracts (see Contracts).

ensures self.len == old(self.len) - 1 || (old(self.len) == 0 && self.len == 0)

Examples#

use collections::list::{List};
use tests::assert;
let xs: List<int> = List::new();
xs.push_front(7);
assert!((xs.pop_front() ?? 0) == 7);
assert!(xs.pop_front().is_none());

See also#

• List: A singly-linked list with constant-time push and pop at the front.
• List::new: Creates an empty list.
• List::size: Returns the number of values.
• List::is_empty: Returns true when the list has no values.
• List::push_front: Adds v at the front.
• List::push_back: Adds v at the back.
• List::peek_front: Returns the front value without removing it, or None when the list is empty.
• List::pop_back: Removes and returns the back value, or None when the list is empty.