`VecDeque`

With the VecDeque in Rust, part of the std collections, we have a ring buffer. The front and back of the VecDeque can be added to or removed from with good performance.

Based on a Vector, the VecDeque helps us maintain the buffer's elements. To add elements, we use push_back or push_front. To remove elements, we use pop_back or pop_front.

Example

This program uses the Rust VecDeque in a variety of ways. It adds to the end and start with push_back and push_front, then loops over the elements.

Part 1 We create a VecDeque with the new() method. We call push_back 3 times and add integers to the buffer.

Part 2 We can use a for-loop to iterate over the elements stored within the VecDeque.

Part 3 Sometimes it can improve performance to use with_capacity to create a VecDeque. Here we also use push_front to add to the buffer's start.

Part 4 We can access the front and back with front() and back(). These return Options, so we can access them in a if-let statement.

Part 5 Sometimes we may need to clone() the VecDeque. We can also convert it to a Vec with the collect method.

Part 6 For removing elements, we can use pop_back and pop_front. We can even rotate elements left and right.

use std::collections::*;

fn main() {
    // Part 1: create VecDeque and add 3 elements to it with push_back.
    let mut v = VecDeque::new();
    v.push_back(100);
    v.push_back(200);
    v.push_back(300);

    // Part 2: loop over VecDeque.
    for element in v {
        println!("Element: {element}");
    }

    // Part 3: create VecDeque with a starting capacity, and use push_front.
    let mut x = VecDeque::with_capacity(10);
    x.push_back("my");
    x.push_back("friend");
    x.push_back("!");
    x.push_front("hello");

    // Part 4: access front and back of VecDeque.
    if let Some(front) = x.front() {
        if let Some(back) = x.back() {
            println!("front = {}; back = {}", front, back);
        }
    }

    // Part 5: clone and convert into a Vec.
    let result = x.clone().into_iter().collect::<Vec<&str>>();
    println!("clone       {:?}", result);

    // Part 6: pop_back and rotate_left.
    x.pop_back();
    println!("pop_back    {:?}", x);
    x.rotate_left(1);
    println!("rotate_left {:?}", x);
}Element: 100
Element: 200
Element: 300
front = hello; back = !
clone       ["hello", "my", "friend", "!"]
pop_back    ["hello", "my", "friend"]
rotate_left ["my", "friend", "hello"]

Summary

As it uses a Vector internally, the VecDeque could be replaced with a Vector. But by using the pre-built VecDeque helper methods, our programs are shorter and easier to maintain.