用 Rust 实现队列

对于rust-primer中实现（https://rustcc.gitbooks.io/rustprimer/content/data-structure/queue.html　）的改进版本，源码如下：

#[derive(Debug)]
struct Queue<T> {
    qdata: Vec<T>,
}

impl <T> Queue<T> {
    fn new() -> Self {
        Queue{ qdata: Vec::new() }
    }

    fn push(&mut self, item: T) {
        self.qdata.push(item);
    }

    fn pop(&mut self) ->Option<T> {
        let l = self.qdata.len();

        if l > 0 {
            let v = self.qdata.remove(0);
            Some(v)
        } else {
            None
        }
    }
}

fn main() {
    let mut q = Queue::new();
    q.push(1);
    q.push(2);
    println!("{:?}", q);

    q.pop();
    println!("{:?}", q);

    q.pop();
    println!("Hello, world!");

    q.pop();
    println!("Hello, world!");
}