lifetime/static #254

2022-06-09T12:33:52Z

giscus[bot]
bot Jun 9, 2022

lifetime/static

Learn Rust with Example, Exercise and real Practice, written with ❤️ by https://course.rs team

https://practice.rs/lifetime/static.html

Sartner · 2022-08-05T08:39:59Z

Sartner
Aug 5, 2022 — with giscus

第六题直接麻了😵

0 replies

3wish · 2022-09-21T15:58:07Z

3wish
Sep 21, 2022 — with giscus

第六题应该怎么理解？

1 reply

tjw123hh Aug 6, 2023 — with giscus

应该是string是'static而&string不为'static

jingth · 2022-10-08T05:13:47Z

jingth
Oct 8, 2022 — with giscus

第6题修改后能编译通过，但不知道对不对。

use std::fmt::Display;

fn main() {
//let mut string = "First".to_owned();

//string.push_str(string.to_uppercase().as_str());

//println!("{}", string);

const string: &str = "FirstFIRST";

print_a(&string);
print_b(&string);
print_c(&string); // Compilation error
print_d(&string); // Compilation error
print_e(&string);
print_f(&string);
print_g(&string); // Compilation error

}

fn print_a<T: Display + 'static>(t: &T) {
println!("{}", t);
}

fn print_b(t: &T)
where
T: Display + 'static,
{
println!("{}", t);
}

fn print_c(t: &'static dyn Display) {
println!("{}", t)
}

fn print_d(t: &'static impl Display) {
println!("{}", t)
}

fn print_e(t: &(dyn Display + 'static)) {
println!("{}", t)
}

fn print_f(t: &(impl Display + 'static)) {
println!("{}", t)
}

fn print_g(t: &'static str) {
println!("{}", t);
}

1 reply

sure2web3 Oct 23, 2022 — with giscus

#[derive(Debug)]
struct Config {
    a: String,
    b: String,
}
static mut config: Option<&mut Config> = None;

/* 让代码工作，但不要修改函数的签名 */
fn init() -> Option<&'static mut Config> {
    Some(Box::leak(Box::new(Config {
        a: "A".to_string(),
        b: "B".to_string(),
    })))
}


fn main() {
    unsafe {
        config = init();

        println!("{:?}",config)
    }
}

roushanyyzz · 2022-10-20T15:04:22Z

roushanyyzz
Oct 20, 2022 — with giscus

抓着一个用：）

use std::fmt::Display;

fn main() {
    let mut string = "First".to_owned();

    string.push_str(string.to_uppercase().as_str());
    print_a(&string);
    print_b(&string);
    print_c(Box::leak(Box::new(string))); // Compilation error
    print_d(Box::leak(Box::new(string))); // Compilation error
    print_e(Box::leak(Box::new(string)));
    print_f(Box::leak(Box::new(string)));
    print_g(Box::leak(Box::new(string))); // Compilation error
}

fn print_a<T: Display + 'static>(t: &T) {
    println!("{}", t);
}

fn print_b<T>(t: &T)
where
    T: Display + 'static,
{
    println!("{}", t);
}

fn print_c(t: &'static dyn Display) {
    println!("{}", t)
}

fn print_d(t: &'static impl Display) {
    println!("{}", t)
}

fn print_e(t: &(dyn Display + 'static)) {
    println!("{}", t)
}

fn print_f(t: &(impl Display + 'static)) {
    println!("{}", t)
}

fn print_g(t: &'static String) {
    println!("{}", t);
}

3 replies

roushanyyzz Oct 20, 2022 — with giscus

果然只是看起来不报错

roushanyyzz Oct 23, 2022 — with giscus

离成功一步之遥

DaZhou-ECHO Mar 17, 2024 — with giscus

很厉害了，只需要clone就行了

sure2web3 · 2022-10-23T10:51:17Z

sure2web3
Oct 23, 2022 — with giscus

第二题

#[derive(Debug)]
struct Config {
a: String,
b: String,
}
static mut config: Option<&mut Config> = None;

/* 让代码工作，但不要修改函数的签名 */
fn init() -> Option<&'static mut Config> {
Some(Box::leak(Box::new(Config {
a: "A".to_string(),
b: "B".to_string(),
})))
}

fn main() {
unsafe {
config = init();

    println!("{:?}",config)
}

}

0 replies

sure2web3 · 2022-10-23T11:19:51Z

sure2web3
Oct 23, 2022 — with giscus

第六题，可以通过编译

use std::fmt::Display;

fn main() {
    let mut string = "First".to_owned();

    string.push_str(string.to_uppercase().as_str());
    print_a(&string);
    print_b(&string);
    print_c(Box::leak(Box::new(string.clone()))); // Compilation error
    print_d(Box::leak(Box::new(string.clone()))); // Compilation error
    print_e(&string);
    print_f(&string);
    print_g(Box::leak(Box::new(string))); // Compilation error
}

fn print_a<T: Display + 'static>(t: &T) {
    println!("{}", t);
}

fn print_b<T>(t: &T)
    where
        T: Display + 'static,
{
    println!("{}", t);
}

fn print_c(t: &'static dyn Display) {
    println!("{}", t)
}

fn print_d(t: &'static impl Display) {
    println!("{}", t)
}

fn print_e(t: &(dyn Display + 'static)) {
    println!("{}", t)
}

fn print_f(t: &(impl Display + 'static)) {
    println!("{}", t)
}

fn print_g(t: &'static String) {
    println!("{}", t);
}

1 reply

roushanyyzz Oct 23, 2022 — with giscus

嗨，原来我忘记加.clone()

liaosunny123 · 2023-01-15T02:26:12Z

liaosunny123
Jan 15, 2023 — with giscus

第一题：

方法1：

/* 使用两种方法填空 */
fn main() {
    let v = "hello";
    need_static(v);

    println!("Success!")
}

fn need_static(r : &'static str) {
    assert_eq!(r, "hello");
}

方法2：

/* 使用两种方法填空 */
fn main() {
    static v:&str = "hello";
    need_static(v);

    println!("Success!")
}

fn need_static(r : &'static str) {
    assert_eq!(r, "hello");
}

第二题：

#[derive(Debug)]
struct Config {
    a: String,
    b: String,
}
static mut config: Option<&mut Config> = None;

/* 让代码工作，但不要修改函数的签名 */
fn init() -> Option<&'static mut Config> {
    Some(Box::leak(Box::new(Config {
        a: "A".to_string(),
        b: "B".to_string(),
    })))
}


fn main() {
    unsafe {
        config = init();

        println!("{:?}",config)
    }
}

第三题：

fn main() {
    
        // 字符串字面量能跟程序活得一样久，因此 `static_string` 的生命周期是 `'static`
        let static_string = "I'm in read-only memory";
        println!("static_string: {}", static_string);

        // 当 `static_string` 超出作用域时，该引用就无法再被使用，但是引用指向的数据( 字符串字面量 ) 依然保存在二进制 binary 所占用的内存中
    

    println!("static_string reference remains alive: {}", static_string);
}

第四题：

无

第五题：

/* 让代码工作 */
use std::fmt::Debug;

fn print_it<T: Debug + 'static>( input: T) {
    println!( "'static value passed in is: {:?}", input );
}

fn print_it1<T:Debug + 'static>( input:&T ) {
    println!( "'static value passed in is: {:?}", input );
}


fn print_it2<T: Debug + 'static>( input: &T) {
    println!( "'static value passed in is: {:?}", input );
}

fn main() {
    // i 是有所有权的数据，并没有包含任何引用，因此它是 'static
    let i = 5;
    print_it(i);

    // 但是 &i 是一个引用，生命周期受限于作用域，因此它不是 'static
    print_it(i);

    print_it1(&i);

    // 但是下面的代码可以正常运行 !
    print_it2(&i);
}

第六题：

use std::fmt::Display;

fn main() {
  let mut string = "First".to_owned();

  string.push_str(string.to_uppercase().as_str());
  print_a(&string);
  print_b(&string);
  print_c(Box::leak(Box::new(string.clone()))); // Compilation error
  print_d(Box::leak(Box::new(string.clone()))); // Compilation error
  print_e(&string);
  print_f(&string);
  print_g(Box::leak(Box::new(string.clone()))); // Compilation error
}

fn print_a<T: Display + 'static>(t: &T) {
  println!("{}", t);
}

fn print_b<T>(t: &T)
where
  T: Display + 'static,
{
  println!("{}", t);
}

fn print_c(t: &'static dyn Display) {
  println!("{}", t)
}

fn print_d(t: &'static impl Display) {
  println!("{}", t)
}

fn print_e(t: &(dyn Display + 'static)) {
  println!("{}", t)
}

fn print_f(t: &(impl Display + 'static)) {
  println!("{}", t)
}

fn print_g(t: &'static String) {
  println!("{}", t);
}

0 replies

tannineo · 2023-03-03T10:41:21Z

tannineo
Mar 3, 2023 — with giscus

关于第四题, 这里的描述是不是有点误导, 并不是强制转变了&NUM的生命周期, 单纯只是绑定了一个新的引用?

比如函数可以写成:

fn coerce_static<'a>(_: &'a i32) -> &'a i32 {
    let x = &NUM;
    x
}

而更进一步main也能直接写成:

fn main() {
    {
        // let lifetime_num = 9;

        // let coerced_static = coerce_static(&lifetime_num);
        let coerced_static = &NUM;

        println!("coerced_static: {}", coerced_static);
    }

    println!("NUM: {} stays accessible!", NUM);
}

coerced_static 本身是一个应用, 他的生命周期就在花括号里面吧, 感觉没有变化.

如果有错希望大家指正, 提前谢谢!

2 replies

tannineo Mar 3, 2023 — with giscus

应用 => 引用

tannineo Mar 3, 2023 — with giscus

哦哦哦, 我可能混淆了 ‘引用本身被销毁的时机’ 和 ’生命周期‘ 的概念.

假如又有一个函数, 尝试用'static:

// 声明一个 static 常量，它拥有 `'static` 生命周期.
static NUM: i32 = 18;

// 返回常量 `Num` 的引用，注意，这里的生命周期从 `'static` 强转为 `'a`
fn coerce_static<'a>(_: &'a i32) -> &'a i32 {
    &NUM
}

fn try_static(_: &'static i32) {
    // do nothing
}

fn main() {
    {
        let lifetime_num = 9;

        let coerced_static = coerce_static(&lifetime_num);
        
        try_static(coerced_static);

        println!("coerced_static: {}", coerced_static);
    }

    println!("NUM: {} stays accessible!", NUM);
}

报错:

   Compiling playground v0.0.1 (/playground)
error[E0597]: `lifetime_num` does not live long enough
  --> src/main.rs:17:44
   |
17 |         let coerced_static = coerce_static(&lifetime_num);
   |                              --------------^^^^^^^^^^^^^-
   |                              |             |
   |                              |             borrowed value does not live long enough
   |                              argument requires that `lifetime_num` is borrowed for `'static`
...
22 |     }
   |     - `lifetime_num` dropped here while still borrowed

For more information about this error, try `rustc --explain E0597`.
error: could not compile `playground` due to previous error

我大概理解第四题的意思了...

ky2312 · 2023-06-06T06:10:05Z

ky2312
Jun 6, 2023 — with giscus

第六题

use std::fmt::Display;

fn main() {
  let mut string = "First".to_owned();

  string.push_str(string.to_uppercase().as_str());
  // 泄露
  let string = Box::leak(Box::new(string));

  print_a(&string);
  print_b(&string);
  print_c(&*string); // Compilation error
  print_d(&*string); // Compilation error
  print_e(&string);
  print_f(&string);
  print_g(&*string); // Compilation error
}

fn print_a<T: Display + 'static>(t: &T) {
  println!("{}", t);
}

fn print_b<T>(t: &T)
where
  T: Display + 'static,
{
  println!("{}", t);
}

fn print_c(t: &'static dyn Display) {
  println!("{}", t)
}

fn print_d(t: &'static impl Display) {
  println!("{}", t)
}

fn print_e(t: &(dyn Display + 'static)) {
  println!("{}", t)
}

fn print_f(t: &(impl Display + 'static)) {
  println!("{}", t)
}

fn print_g(t: &'static String) {
  println!("{}", t);
}

0 replies

coderLanlan · 2023-07-24T05:54:26Z

coderLanlan
Jul 24, 2023 — with giscus

修改方法，可以通过编译
use std::fmt::Display;

fn main() {
let mut string = "First".to_owned();

string.push_str(string.to_uppercase().as_str());
print_a(&string);
print_b(&string);
print_c(&string); // Compilation error
print_d(&string); // Compilation error
print_e(&string);
print_f(&string);
print_g(&string); // Compilation error

}

fn print_a<T: Display + 'static>(t: &T) {
println!("{}", t);
}

fn print_b(t: &T)
where
T: Display + 'static,
{
println!("{}", t);
}

fn print_c(t: &dyn Display) {
println!("{}", t)
}

fn print_d(t: &impl Display) {
println!("{}", t)
}

fn print_e(t: &(dyn Display + 'static)) {
println!("{}", t)
}

fn print_f(t: &(impl Display + 'static)) {
println!("{}", t)
}

fn print_g(t: &str) {
println!("{}", t);
}

0 replies

Jamin1995 · 2023-08-19T00:37:56Z

Jamin1995
Aug 19, 2023 — with giscus

use std::fmt::Display;

fn main() {
let mut string = "First".to_owned();

string.push_str(string.to_uppercase().as_str());
let string = Box::leak(Box::new(string)); //暴力创建一个 &'static String

print_a(string);
print_b(string);
print_c(string); // Compilation error
print_d(string); // Compilation error
print_e(string);
print_f(string);
print_g(string); // Compilation error
}

fn print_a<T: Display + 'static>(t: &T) {
println!("{}", t);
}

fn print_b(t: &T)
where
T: Display + 'static,
{
println!("{}", t);
}

fn print_c(t: &'static dyn Display) {
println!("{}", t)
}

fn print_d(t: &'static impl Display) {
println!("{}", t)
}

fn print_e(t: &(dyn Display + 'static)) {
println!("{}", t)
}

fn print_f(t: &(impl Display + 'static)) {
println!("{}", t)
}

fn print_g(t: &'static String) {
println!("{}", t);
}

0 replies

CListery · 2023-08-31T08:01:31Z

CListery
Aug 31, 2023 — with giscus

第六通杀：

Box::leak(Box::new(string.clone()))

0 replies

5cjMMw · 2024-01-07T03:14:54Z

5cjMMw
Jan 7, 2024 — with giscus

看到一篇帖子：https://www.jianshu.com/p/500ed3635a41
这里面有一段话我觉得对'static约束解释的很好："The 'static bound on a type doesn't control how long that object lives; it controls the allowable lifetime of references that object holds."
第6题感觉就是在考察'static这个约束到底是在约束T(String)还是&T(&String)，如果按照上面这句话来解释，当'static用来约束String时，是不会出问题的，因为String中不包含引用类型，'static只关心对象中的包含的引用类型的生命周期，显然在第6题中&string并不满足'static，像第5题中的&i一样
以上是一些个人理解，如有错误，希望大佬们指出🙏

0 replies

Hihongboyang · 2024-05-23T09:18:49Z

Hihongboyang
May 23, 2024 — with giscus

第三题诶，就是玩

fn main() {
    let static_string = "I'm in read-only memory";
    let ptr_s: *const u8 = static_string.as_ptr();
    let len = static_string.len();
    
    unsafe {
        // 将裸指针和长度转换为切片
        let slice = std::slice::from_raw_parts(ptr_s, len);
        
        // 将切片转换为字符串
        println!("static_string: {}", std::str::from_utf8(slice).unwrap())
    }
}

0 replies

wty92911 · 2024-11-04T08:55:45Z

wty92911
Nov 4, 2024 — with giscus

&'static T ，static修饰的是引用，因此无论是&String还是 dyn/impl Display 都无法通过编译。
(&'static impl Display = &'static T ... where T: Display)。
T: 'static ... (&T) ，static修饰的是T本身。

1 reply

wty92911 Nov 4, 2024 — with giscus

而String类型中不包含任何引用，因此&String... String: 'static 是可以通过编译的

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

lifetime/static #254

{{title}}

Replies: 15 comments 9 replies

{{title}}

{{title}}

{{title}}

{{editor}}'s edit

{{editor}}'s edit

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

Select a reply

lifetime/static #254

giscus[bot] bot Jun 9, 2022

lifetime/static

Replies: 15 comments · 9 replies

Sartner Aug 5, 2022 — with giscus

3wish Sep 21, 2022 — with giscus

tjw123hh Aug 6, 2023 — with giscus

jingth Oct 8, 2022 — with giscus

sure2web3 Oct 23, 2022 — with giscus

roushanyyzz Oct 20, 2022 — with giscus

roushanyyzz Oct 20, 2022 — with giscus

roushanyyzz Oct 23, 2022 — with giscus

DaZhou-ECHO Mar 17, 2024 — with giscus

sure2web3 Oct 23, 2022 — with giscus

sure2web3 Oct 23, 2022 — with giscus

第六题，可以通过编译

roushanyyzz Oct 23, 2022 — with giscus

liaosunny123 Jan 15, 2023 — with giscus

第一题：

第二题：

第三题：

第四题：

第五题：

第六题：

tannineo Mar 3, 2023 — with giscus

tannineo Mar 3, 2023 — with giscus

tannineo Mar 3, 2023 — with giscus

ky2312 Jun 6, 2023 — with giscus

第六题

coderLanlan Jul 24, 2023 — with giscus

Jamin1995 Aug 19, 2023 — with giscus

CListery Aug 31, 2023 — with giscus

5cjMMw Jan 7, 2024 — with giscus

Hihongboyang May 23, 2024 — with giscus

第三题 诶，就是玩

wty92911 Nov 4, 2024 — with giscus

wty92911 Nov 4, 2024 — with giscus

giscus[bot]
bot Jun 9, 2022

Replies: 15 comments 9 replies

Sartner
Aug 5, 2022 — with giscus

3wish
Sep 21, 2022 — with giscus

jingth
Oct 8, 2022 — with giscus

roushanyyzz
Oct 20, 2022 — with giscus

sure2web3
Oct 23, 2022 — with giscus

sure2web3
Oct 23, 2022 — with giscus

liaosunny123
Jan 15, 2023 — with giscus

tannineo
Mar 3, 2023 — with giscus

ky2312
Jun 6, 2023 — with giscus

coderLanlan
Jul 24, 2023 — with giscus

Jamin1995
Aug 19, 2023 — with giscus

CListery
Aug 31, 2023 — with giscus

5cjMMw
Jan 7, 2024 — with giscus

Hihongboyang
May 23, 2024 — with giscus

第三题诶，就是玩

wty92911
Nov 4, 2024 — with giscus