Rust Circular Queue Implementation from https://www.reddit.com/r/learnrust/comments/99ctqv/how_to_reference_struct_elements/

main.rs

pub struct CircularQueue<T> {
    queue: Vec<Option<T>>,
    head: usize,
    tail: usize,
    max_capacity: usize,
    count: usize,
}

impl<T> CircularQueue<T> {
    pub fn new(size: usize) -> CircularQueue<T> {
        CircularQueue {
            queue: Vec::with_capacity(size),
            head: 0,
            tail: 0,
            max_capacity: size,
            count: 0
        }
    }

    fn is_full(&self) -> bool {
        self.count == self.max_capacity
    }

    fn is_empty(&self) -> bool {
        self.count == 0
    }

    pub fn enqueue(&mut self, item: T) -> Result<(), String>{
        if self.is_full() {
            return Err("Queue is full!".to_owned())
        }
        self.queue.insert(self.tail, Some(item));
        self.tail = (self.tail + 1) % self.max_capacity;
        self.count += 1;
        Ok(())
    }

    pub fn dequeue(&mut self) -> Result<T, String> {
        if self.is_empty() {
            return Err("Queue is empty!".to_owned())
        }
        let item = std::mem::replace(&mut self.queue[self.head], None);
        self.head = (self.head + 1) % self.max_capacity;
        self.count -= 1;
        Ok(item.unwrap())
    }
}


fn main() {
    let mut q = CircularQueue::<usize>::new(2);
    q.enqueue(123).expect("Item 123 should be added");
    println!("q.dequeue() == {}", q.dequeue().expect("Could not dequeue item"));
}