study_rust_example/generic_traits_lifetime/
lifetime_study.rs

1fn outside_scope() {
2    let r;
3    //{
4    let x = 5;
5    // error[E0597]: `x` does not live long enough
6    // 解法将x的生命周期拓展到一样的函数体
7    r = &x;
8    //}
9    println!("r {}", r);
10}
11
12/*
13error[E0106]: missing lifetime specifier
14  --> src/generic_traits_lifetime/lifetime_study.rs:12:38
15   |
1612 | fn longer(str1: &str, str2: &str) -> &str {
17   |                 ----        ----     ^ expected named lifetime parameter
18   = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `str1` or `str2`
19help: consider introducing a named lifetime parameter
20   |
2112 | fn longer<'a>(str1: &'a str, str2: &'a str) -> &'a str {
22   |          ++++        ++             ++          ++
23*/
24// fn longer(str1: &str, str2: &str) -> &str {
25fn longer<'a>(str1: &'a str, str2: &'a str) -> &'a str {
26    if str1.len() >= str2.len() {
27        str1
28    } else {
29        str2
30    }
31}
32
33struct Score<'a> {
34    name: &'a str,
35    score: &'a i32,
36}
37
38impl<'a> Score<'a> {
39    // [规则3]：因为参数之一是 &self ，所以返回类型获取 &self 的生命周期
40    fn get_score(&self) -> &i32 {
41        self.score
42    }
43}
44
45// 能编译过的原因是1.0版本以后，引入了生命周期省略原则，对一些通用确定的情况可以省略繁琐的定义
46fn first_world(str: &str) -> &str {
47    for (index, &item) in str.as_bytes().iter().enumerate() {
48        if item == b' ' {
49            return &str[..index];
50        }
51    }
52    return &str;
53}
54/*
55    [rule1] 转换为：fn first_world<'a>(str: &'a str) -> &str {
56    [rule2] 转换为：fn first_world<'a>(str: &'a str) -> &'a str {
57*/
58
59pub fn lifetime_kown_study<'a>() {
60    outside_scope();
61    let num1: &i32;
62    let num2: &'a i32;
63    let num3: &'a mut i32;
64    let str_result: &str;
65    let str1 = String::from("hello rust lifetime.");
66    {
67        let str2 = String::from("world.");
68        str_result = longer(&str1, &str2);
69        println!("str longer: {}", str_result);
70    }
71    // error[E0597]: `str2` does not live long enough
72    // println!("str_result: {}", str_result);
73
74    let s: &'static str = "test 'static";
75}
study_rust_example/generic_traits_lifetime/lifetime_study.rs

study_rust_example/generic_traits_lifetime/
lifetime_study.rs
