Rust

2022-10-07  本文已影响0人  谭英智

解决了什么问题

语言基础

所有权

作用域

变量离开作用域，则自动释放内存

移动

let s1 = String::from("hello");
le s2 = s1; //类似c++的move
println!("{}, world!", s1); //编译失败
rust-move
克隆 
let s1 = String::from("hello");
let s2 = s1.clone(); //深拷贝

println!("s1 = {}, s2 = {}", s1, s2);

引用

要么 只能有一个可变引用，要么 只能有多个不可变引用 ，为了解决数据竞争问题。rust通过编译来做这些限制

fn main() {
    let s1 = String::from("hello");

    let len = calculate_length(&s1);

    println!("The length of '{}' is {}.", s1, len);
}

fn calculate_length(s: &String) -> usize { //常量引用
    s.len()
}


fn main() {
    let mut s = String::from("hello");

    change(&mut s);
}

fn change(some_string: &mut String) { //可变引用
    some_string.push_str(", world");
}

悬垂引用

fn dangle() -> &String {
    let s = String::from("hello");

    &s //编译失败
}

slice

返回string的一段

let s = String::from("hello world");

let hello = &s[0..=4];
let world = &s[6..=10];
rust-slice 
fn first_word(s: &String) -> &str {
    let bytes = s.as_bytes();

    for (i, &item) in bytes.iter().enumerate() {
        if item == b' ' {
            return &s[0..i];
        }
    }

    &s[..]
}

fn main() {
    let mut s = String::from("hello world");

    let word = first_word(&s);

    s.clear(); // 编译失败，内存已经被清空，word不再有效

    println!("the first word is: {}", word);
}

结构体

# #[derive(Debug)]
# struct Rectangle {
#     width: u32,
#     height: u32,
# }
#
impl Rectangle { 
    fn area(&self) -> u32 { //成员函数
        self.width * self.height
    }
}

impl Rectangle {
    fn can_hold(&self, other: &Rectangle) -> bool {
        self.width > other.width && self.height > other.height
    }
}
fn main() {
    let rect1 = Rectangle { width: 30, height: 50 };
    let rect2 = Rectangle { width: 10, height: 40 };
    let rect3 = Rectangle { width: 60, height: 45 };

    println!("Can rect1 hold rect2? {}", rect1.can_hold(&rect2));
    println!("Can rect1 hold rect3? {}", rect1.can_hold(&rect3));
}

枚举

enum IpAddrKind {
    V4,
    V6,
}
let four = IpAddrKind::V4;

enum IpAddr {
    V4(String),
    V6(String),
}

let home = IpAddr::V4(String::from("127.0.0.1"));

let loopback = IpAddr::V6(String::from("::1"));

枚举与控制流：

# #[derive(Debug)]
# enum UsState {
#    Alabama,
#    Alaska,
# }
#
# enum Coin {
#    Penny,
#    Nickel,
#    Dime,
#    Quarter(UsState),
# }
#
fn value_in_cents(coin: Coin) -> u32 {
    match coin {
        Coin::Penny => 1,
        Coin::Nickel => 5,
        Coin::Dime => 10,
        Coin::Quarter(state) => {
            println!("State quarter from {:?}!", state);
            25
        },
    }
}

Option枚举

它用来表示一个变量是Null或者有值

enum Option {
    Some(T),
    None,
}
let some_number = Some(5);
let some_string = Some("a string");

let absent_number: Option<i32> = None;


fn plus_one(x: Option<i32>) -> Option<i32> {
    match x {
        None => None,
        Some(i) => Some(i + 1),
    }
}

let five = Some(5);
let six = plus_one(five);
let none = plus_one(None);


let some_u8_value = Some(0u8);
if let Some(3) = some_u8_value {
    println!("three");
}

集合

vector

变长数组

let v: Vec<i32> = Vec::new();
let v = vec![1, 2, 3];
v.push(5); //追加
v.pop();
let third: &i32 = &v[2];
let does_not_exist = &v[100]; //panic
let does_not_exist = v.get(100); //返回None
let first = &v[0]; //借用
v.push(6); //error, first的内存可能已经被释放

遍历

let v = vec![100, 32, 57];
for i in &v { //常量引用
    println!("{}", i);
}

let mut v = vec![100, 32, 57];
for i in &mut v { //可变引用
    *i += 50;
}

string

新建：

let mut s = String::new();
let s = "initial contents".to_string();
let s = String::from("initial contents");

追加：

s.push_str("bar");

拼接：

let s1 = String::from("Hello, ");
let s2 = String::from("world!");
let s3 = s1 + &s2; // 注意 s1 被移动了，不能继续使用

string的add函数原型如下：

fn add(self, s: &str) -> String {

s2以常量引用的方式传入add

s1以移动的方式传入add

s1不再拥有所有权

所有权被移交到s3中

let s1 = String::from("tic");
let s2 = String::from("tac");
let s3 = String::from("toe");

let s = format!("{}-{}-{}", s1, s2, s3);

通过format，s1 s2 s3的所有权都得以保留

索引

let s1 = String::from("hello");
let h = s1[0]; //error

字符串不能索引，因为String支持的编码类型复杂

遍历

for c in "नमस्ते".chars() {
    println!("{}", c);
}
for b in "नमस्ते".bytes() {
    println!("{}", b);
}

哈希map

新建

use std::collections::HashMap;
let mut map = HashMap::new();

插入

let field_name = String::from("Favorite color");
let field_value = String::from("Blue");
map.insert(field_name, field_value);
// 这里 field_name 和 field_value 不再有效
map.insert(String::from("Hate"), String::from("Red"));
map.entry(String::from("OK")).or_insert(String::from("Yello")); //只有键不存在时插入，返回value的指针
println!("{:?}", map);

访问

let name = String::from("OK");
let color = map.get(&name);
for (key, value) in &map { //常量引用s
    println!("{}: {}", key, value);
}

错误

panic

不可恢复异常，程序会输出bt

fn main() {
    panic!("crash and burn");
}
fn main() {
    let v = vec![1, 2, 3];

    v[99]; //越界，panic
}

result

可恢复错误

use std::io;
use std::io::Read;
use std::fs::File;

fn read_username_from_file() -> Result<String, io::Error> {
    let f = File::open("hello.txt");

    let mut f = match f {
        Ok(file) => file,
        Err(e) => return Err(e),
    };

    let mut s = String::new();

    match f.read_to_string(&mut s) {
        Ok(_) => Ok(s),
        Err(e) => Err(e),
    }
}

泛型

struct Point<T> {
    x: T,
    y: T,
}

impl<T> Point<T> {
    fn x(&self) -> &T {
        &self.x
    }
}

fn main() {
    let p = Point { x: 5, y: 10 };

    println!("p.x = {}", p.x());
}

impl Point<f32> { //对f32单态化后，实现函数
    fn distance_from_origin(&self) -> f32 {
        (self.x.powi(2) + self.y.powi(2)).sqrt()
    }
}

trait

接口

 pub trait Summary {
     fn summarize(&self) -> String;
 }

pub struct NewsArticle {
    pub headline: String,
    pub location: String,
    pub author: String,
    pub content: String,
}

impl Summary for NewsArticle {
    fn summarize(&self) -> String {
        format!("{}, by {} ({})", self.headline, self.author, self.location)
    }
}

pub struct Tweet {
    pub username: String,
    pub content: String,
    pub reply: bool,
    pub retweet: bool,
}

impl Summary for Tweet {
    fn summarize(&self) -> String { //多态
        format!("{}: {}", self.username, self.content)
    }
}

let tweet = Tweet { //实例化
    username: String::from("horse_ebooks"),
    content: String::from("of course, as you probably already know, people"),
    reply: false,
    retweet: false,
};

println!("1 new tweet: {}", tweet.summarize());

接口作为参数

pub fn notify(item: impl Summary) {
    println!("Breaking news! {}", item.summarize());
}
fn some_function<T, U>(t: T, u: U) -> i32
    where T: Display + Clone,
          U: Clone + Debug
{
}

fn returns_summarizable(switch: bool) -> impl Summary {
    if switch {
        NewsArticle {
            headline: String::from("Penguins win the Stanley Cup Championship!"),
            location: String::from("Pittsburgh, PA, USA"),
            author: String::from("Iceburgh"),
            content: String::from("The Pittsburgh Penguins once again are the best
            hockey team in the NHL."),
        }
    } else {
        Tweet {
            username: String::from("horse_ebooks"),
            content: String::from("of course, as you probably already know, people"),
            reply: false,
            retweet: false,
        }
    }
}

泛型与trait

Copy代表类型T可以被拷贝

PartialOrd代表T为数字类型

Display 代表T可以被打印

fn largest<T: PartialOrd + Copy>(list: &[T]) -> T {
    let mut largest = list[0];

    for &item in list.iter() {
        if item > largest {
            largest = item;
        }
    }

    largest
}

fn main() {
    let number_list = vec![34, 50, 25, 100, 65];

    let result = largest(&number_list);
    println!("The largest number is {}", result);

    let char_list = vec!['y', 'm', 'a', 'q'];

    let result = largest(&char_list);
    println!("The largest char is {}", result);
}

生命周期省略

fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}

智能指针

以引用计数来管理内存

在堆创建数据

fn main() {
    let b = Box::new(5);
    println!("b = {}", b);
}

创建递归类型

enum List {
    Cons(i32, Box<List>),
    Nil,
}

use crate::List::{Cons, Nil};

fn main() {
    let list = Cons(1,
        Box::new(Cons(2,
            Box::new(Cons(3,
                Box::new(Nil))))));
}

提早释放

fn main() {
    let c = CustomSmartPointer { data: String::from("some data") };
    println!("CustomSmartPointer created.");
    drop(c);
    println!("CustomSmartPointer dropped before the end of main.");
}

增加引用

enum List {
    Cons(i32, Box<List>),
    Nil,
}

use crate::List::{Cons, Nil};

fn main() {
    let a = Cons(5,
        Box::new(Cons(10,
            Box::new(Nil))));
    let b = Cons(3, Box::new(a)); //move
    let c = Cons(4, Box::new(a)); //error
}

正确的做法：

enum List {
    Cons(i32, Rc<List>),
    Nil,
}

use crate::List::{Cons, Nil};
use std::rc::Rc;

fn main() {
    let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil)))));
    let b = Cons(3, Rc::clone(&a)); //增加计数，只读引用，数据不可变
    let c = Cons(4, Rc::clone(&a)); //增加计数，只读引用，数据不可变
}

可变引用，计数增加：

enum List {
    Cons(Rc<RefCell<i32>>, Rc<List>),
    Nil,
}

use crate::List::{Cons, Nil};
use std::rc::Rc;
use std::cell::RefCell;

fn main() {
    let value = Rc::new(RefCell::new(5));

    let a = Rc::new(Cons(Rc::clone(&value), Rc::new(Nil)));

    let b = Cons(Rc::new(RefCell::new(6)), Rc::clone(&a)); 
    let c = Cons(Rc::new(RefCell::new(10)), Rc::clone(&a));

    *value.borrow_mut() += 10;

    println!("a after = {:?}", a);
    println!("b after = {:?}", b);
    println!("c after = {:?}", c);
}

解决循环引用

使用weak代替Rc

并行编程

多线程

use std::thread;
use std::time::Duration;

fn main() {
    let handle = thread::spawn(|| {
        for i in 1..10 {
            println!("hi number {} from the spawned thread!", i);
            thread::sleep(Duration::from_millis(1));
        }
    });

    for i in 1..5 {
        println!("hi number {} from the main thread!", i);
        thread::sleep(Duration::from_millis(1));
    }

    handle.join().unwrap();
}

线程使用主线程变量

use std::thread;

fn main() {
    let v = vec![1, 2, 3];

    let handle = thread::spawn(move || {
        println!("Here's a vector: {:?}", v);
    });

    handle.join().unwrap();
}

消息传递

# use std::thread;
# use std::sync::mpsc;
# use std::time::Duration;
#
# fn main() {
// --snip--

let (tx, rx) = mpsc::channel();

let tx1 = mpsc::Sender::clone(&tx); //多生产者
thread::spawn(move || {
    let vals = vec![
        String::from("hi"),
        String::from("from"),
        String::from("the"),
        String::from("thread"),
    ];

    for val in vals {
        tx1.send(val).unwrap();
        thread::sleep(Duration::from_secs(1));
    }
});

thread::spawn(move || {
    let vals = vec![
        String::from("more"),
        String::from("messages"),
        String::from("for"),
        String::from("you"),
    ];

    for val in vals {
        tx.send(val).unwrap(); //val所有权转移
        thread::sleep(Duration::from_secs(1));
    }
});

for received in rx {
    println!("Got: {}", received);
}

// --snip--
# }

多线程共享可变变量

use std::sync::{Mutex, Arc};
use std::thread;

fn main() {
    let counter = Arc::new(Mutex::new(0)); //Arc是带有原子性的智能指针，Rc是不带原子性的智能指针
    let mut handles = vec![];

    for _ in 0..10 {
        let counter = Arc::clone(&counter);
        let handle = thread::spawn(move || {
            let mut num = counter.lock().unwrap();

            *num += 1;
        });
        handles.push(handle);
    }

    for handle in handles {
        handle.join().unwrap();
    }

    println!("Result: {}", *counter.lock().unwrap());
}
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