VecDeque::pop_front

pub fn pop_front() -> Option<T>

use collections::deque::{VecDeque};

Removes and returns the front value, or None when the deque is empty.

Called on a VecDeque 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::deque::{VecDeque};
use tests::assert;
let q: VecDeque<int> = VecDeque::new();
q.push_back(1);
q.push_back(2);
assert!((q.pop_front() ?? 0) == 1);
assert!((q.pop_front() ?? 0) == 2);
assert!(q.pop_front().is_none());

See also#

• VecDeque: A double-ended queue: constant-time push and pop at both ends.
• VecDeque::with_capacity: Empty deque with ring capacity rounded up to the next power of two (min 8).
• VecDeque::new: Empty deque with default capacity 8.
• VecDeque::size: Returns the number of values.
• VecDeque::is_empty: Returns true when the deque has no values.
• VecDeque::capacity: Returns how many values fit before the ring buffer grows.
• VecDeque::push_back: Adds v at the back.
• VecDeque::push_front: Adds v at the front.