头条地址：https://www.ixigua.com/i6765442674582356483github地址：见【了解更多】，今天小编就来聊一聊关于rust编程实战?接下来我们就一起去研究一下吧!
rust编程实战
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介绍Option类型代表了一个可选的值，每个Option要么是一个Some中包含一个值，要么是一个None。Option的定义如下：
pub enum Option<T> { None, Some(T),}
Option主要有以下一些用法：
初始化值；作为在整个输入范围内没有定义的函数的返回值；作为返回值，用None表示出现的简单错误；作为结构体的可选字段；作为结构体中可借出或者是可载入的字段；作为函数的可选参数；代表空指针；用作复杂情况的返回值。此处，我们举例说明一下“作为结构体可借出或者是可载入的字段”。
use std::thread;use std::time::Duration;struct Worker { thread: thread::JoinHandle<()>,}impl Worker { fn new() -> Worker { let thread = thread::spawn(move || { println!("start sleep 10 secs ..."); thread::sleep(Duration::from_secs(10)); }); Worker { thread: thread, } }}struct ThreadPool { workers: Vec<Worker>,}impl ThreadPool { fn new(size: usize) -> ThreadPool { assert!(size > 0); let mut workers = Vec::with_capacity(size); for _ in 0..size { workers.push(Worker::new()); } ThreadPool { workers } }}impl Drop for ThreadPool { fn drop(&mut self) { for worker in &mut self.workers { worker.thread.join().unwrap();//报错，无法编译，thread也无法实现copy trait println!("worker thread finished!"); } }}fn main() { let _pool = ThreadPool::new(3); println!("Hello, world!");}
上述例子中，实现了一个不完整的线程池，在Worker中，有一个字段为线程的句柄。当线程池对象drop时，无法使用mut对象中成员的引用（即通过&mut self.workers取出worker，在调用worker.thread.join()）。为了解决此问题，我们可以将Worker结构体修改如下：
struct Worker { // thread: thread::JoinHandle<()>, thread: Option<thread::JoinHandle<()>>,}
完整代码为：
use std::thread;use std::time::Duration;struct Worker { // thread: thread::JoinHandle<()>, thread: Option<thread::JoinHandle<()>>,}impl Worker { fn new() -> Worker { let thread = thread::spawn(move || { println!("start sleep 10 secs ..."); thread::sleep(Duration::from_secs(10)); }); Worker { // thread: thread, thread: Some(thread), } }}struct ThreadPool { workers: Vec<Worker>,}impl ThreadPool { fn new(size: usize) -> ThreadPool { assert!(size > 0); let mut workers = Vec::with_capacity(size); for _ in 0..size { workers.push(Worker::new()); } ThreadPool { workers } }}impl Drop for ThreadPool { fn drop(&mut self) { for worker in &mut self.workers { // worker.thread.join().unwrap(); // println!("worker thread finished!"); if let Some(thread) = worker.thread.take() {//此处将thread从Worker的thread字段的Option中拿出来，使用了“Option类型作为结构体中可借出或者是可载入的字段” thread.join().unwrap(); println!("worker thread finished!"); } } }}fn main() { let _pool = ThreadPool::new(3); println!("Hello, world!");}
在ThreadPool的drop实现中，通过option的take方法，将thread从worker中移出，然后调用join，成功解决问题。
方法is_somepub fn is_some(&self) -> bool当Option中有值时，返回true。is_nonepub fn is_none(&self) -> bool当Option为None时，返回true。containspub fn contains<U>(&self, x: &U) -> bool where U: PartialEq<T>, 当Some中包含给定的值时，返回true。这个是nightly API。//示例 #![feature(option_result_contains)] let x: Option<u32> = Some(2); assert_eq!(x.contains(&2), true); let x: Option<u32> = Some(3); assert_eq!(x.contains(&2), false);as_refpub fn as_ref(&self) -> Option<&T>将&Option<T> 转换为Option<&T>//例子 let text: Option<String> = Some("Hello, world!".to_string()); let text_length: Option<usize> = text.as_ref().map(|s| s.len()); println!("still can print text: {:?}", text);takepub fn take(&mut self) -> Option<T>把值从Option中拿出来，留下None。let mut x = Some(2); let y = x.take(); assert_eq!(x, None); assert_eq!(y, Some(2)); let mut x: Option<u32> = None; let y = x.take(); assert_eq!(x, None); assert_eq!(y, None);copiedpub fn copied(self) -> Option<T>从Option<&T>得到Option<T>(通过复制来实现)let x = 12; let opt_x = Some(&x); assert_eq!(opt_x, Some(&12)); let copied = opt_x.copied(); assert_eq!(copied, Some(12));clonedpub fn cloned(self) -> Option<T>从Option<&T>得到Option<T>(通过克隆来实现)let x = 12; let opt_x = Some(&x); assert_eq!(opt_x, Some(&12)); let cloned = opt_x.cloned(); assert_eq!(cloned, Some(12));,
