examples/queue/src/lib.rs at master · ProgrammingRust/examples · GitHub

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#![warn(rust_2018_idioms)]

#![allow(elided_lifetimes_in_paths)]

/// A first-in, first-out queue of characters.

pub struct Queue {

older: Vec<char>, // older elements, eldest last.

younger: Vec<char> // younger elements, youngest last.

}

impl Queue {

/// Push a character onto the back of a queue.

pub fn push(&mut self, c: char) {

self.younger.push(c);

}

/// Pop a character off the front of a queue. Return `Some(c)` if there

/// was a character to pop, or `None` if the queue was empty.

pub fn pop(&mut self) -> Option<char> {

if self.older.is_empty() {

if self.younger.is_empty() {

return None;

}

// Bring the elements in younger over to older, and put them in

// the promised order.

use std::mem::swap;

swap(&mut self.older, &mut self.younger);

self.older.reverse();

}

// Now older is guaranteed to have something. Vec's pop method

// already returns an Option, so we're set.

self.older.pop()

}

#[test]

fn test_push_pop() {

let mut q = Queue { older: Vec::new(), younger: Vec::new() };

q.push('0');

q.push('1');

assert_eq!(q.pop(), Some('0'));

q.push('∞');

assert_eq!(q.pop(), Some('1'));

assert_eq!(q.pop(), Some('∞'));

assert_eq!(q.pop(), None);

(&mut q).push('0');

(&mut q).push('1');

assert_eq!(q.pop(), Some('0'));

assert_eq!(q.pop(), Some('1'));

}

impl Queue {

pub fn is_empty(&self) -> bool {

self.older.is_empty() && self.younger.is_empty()

}

#[test]

fn test_is_empty() {

let mut q = Queue { older: Vec::new(), younger: Vec::new() };

assert!(q.is_empty());

q.push('☉');

assert!(!q.is_empty());

q.pop();

assert!(q.is_empty());

}

impl Queue {

pub fn split(self) -> (Vec<char>, Vec<char>) {

(self.older, self.younger)

}

#[test]

fn test_split() {

let mut q = Queue { older: Vec::new(), younger: Vec::new() };

q.push('P');

q.push('D');

assert_eq!(q.pop(), Some('P'));

q.push('X');

let (older, younger) = q.split();

// q is now uninitialized.

assert_eq!(older, vec!['D']);

assert_eq!(younger, vec!['X']);

}

impl Queue {

pub fn new() -> Queue {

Queue { older: Vec::new(), younger: Vec::new() }

}

#[test]

fn test_new() {

let mut q = Queue::new();

q.push('*');

q.push('1');

assert_eq!(q.pop(), Some('*'));

q.push('∞');

assert_eq!(q.pop(), Some('1'));

assert_eq!(q.pop(), Some('∞'));

assert_eq!(q.pop(), None);

}

examples/queue/src/lib.rs at master · ProgrammingRust/examples · GitHub

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