2022-02-25 08:57:13 -06:00
|
|
|
|
# 引用和借用
|
|
|
|
|
|
|
|
|
|
### 引用
|
|
|
|
|
🌟
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
fn main() {
|
|
|
|
|
let x = 5;
|
|
|
|
|
// 填写空白处
|
|
|
|
|
let p = __;
|
|
|
|
|
|
|
|
|
|
println!("x 的内存地址是 {:p}", p); // output: 0x16fa3ac84
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
🌟
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
fn main() {
|
|
|
|
|
let x = 5;
|
|
|
|
|
let y = &x;
|
|
|
|
|
|
|
|
|
|
// 只能修改以下行
|
|
|
|
|
assert_eq!(5, y);
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
🌟
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
// 修复错误
|
|
|
|
|
fn main() {
|
|
|
|
|
let mut s = String::from("hello, ");
|
|
|
|
|
|
|
|
|
|
borrow_object(s)
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
fn borrow_object(s: &String) {}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
🌟
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
// 修复错误
|
|
|
|
|
fn main() {
|
|
|
|
|
let mut s = String::from("hello, ");
|
|
|
|
|
|
|
|
|
|
borrow_object(&s)
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
fn borrow_object(s: &mut String) {}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
🌟🌟
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
fn main() {
|
|
|
|
|
let mut s = String::from("hello, ");
|
|
|
|
|
|
|
|
|
|
// 填写空白处,让代码工作
|
|
|
|
|
let p = __;
|
|
|
|
|
|
|
|
|
|
p.push_str("world");
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
#### ref
|
|
|
|
|
`ref` 与 `&` 类似,可以用来获取一个值的引用,但是它们的用法有所不同。
|
|
|
|
|
|
|
|
|
|
🌟🌟🌟
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
fn main() {
|
|
|
|
|
let c = '中';
|
|
|
|
|
|
|
|
|
|
let r1 = &c;
|
|
|
|
|
// 填写空白处,但是不要修改其它行的代码
|
|
|
|
|
let __ r2 = c;
|
|
|
|
|
|
|
|
|
|
assert_eq!(*r1, *r2);
|
|
|
|
|
|
|
|
|
|
// 判断两个内存地址的字符串是否相等
|
|
|
|
|
assert_eq!(get_addr(r1),get_addr(r2));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
// 获取传入引用的内存地址的字符串形式
|
|
|
|
|
fn get_addr(r: &char) -> String {
|
|
|
|
|
format!("{:p}", r)
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
### 借用规则
|
|
|
|
|
🌟
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
// 移除代码某个部分,让它工作
|
|
|
|
|
// 你不能移除整行的代码!
|
|
|
|
|
fn main() {
|
|
|
|
|
let mut s = String::from("hello");
|
|
|
|
|
|
|
|
|
|
let r1 = &mut s;
|
|
|
|
|
let r2 = &mut s;
|
|
|
|
|
|
|
|
|
|
println!("{}, {}", r1, r2);
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
#### 可变性
|
|
|
|
|
🌟 错误: 从可不用对象借用可用
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
fn main() {
|
|
|
|
|
// 通过修改下面一行代码来修复错误
|
|
|
|
|
let s = String::from("hello, ");
|
|
|
|
|
|
|
|
|
|
borrow_object(&mut s)
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
fn borrow_object(s: &mut String) {}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
🌟🌟 Ok: 从可变对象借用不可变
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
// 下面的代码没有任何错误
|
|
|
|
|
fn main() {
|
|
|
|
|
let mut s = String::from("hello, ");
|
|
|
|
|
|
|
|
|
|
borrow_object(&s);
|
|
|
|
|
|
|
|
|
|
s.push_str("world");
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
fn borrow_object(s: &String) {}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
### NLL
|
|
|
|
|
🌟🌟
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
// 注释掉一行代码让它工作
|
|
|
|
|
fn main() {
|
|
|
|
|
let mut s = String::from("hello, ");
|
|
|
|
|
|
|
|
|
|
let r1 = &mut s;
|
|
|
|
|
r1.push_str("world");
|
|
|
|
|
let r2 = &mut s;
|
|
|
|
|
r2.push_str("!");
|
|
|
|
|
|
|
|
|
|
println!("{}",r1);
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
🌟🌟🌟
|
|
|
|
|
```rust,editable
|
|
|
|
|
|
|
|
|
|
fn main() {
|
|
|
|
|
let mut s = String::from("hello, ");
|
|
|
|
|
|
|
|
|
|
let r1 = &mut s;
|
|
|
|
|
let r2 = &mut s;
|
|
|
|
|
|
|
|
|
|
// 在下面增加一行代码人为制造编译错误:cannot borrow `s` as mutable more than once at a time
|
|
|
|
|
// 你不能同时使用 r1 和 r2
|
|
|
|
|
}
|
|
|
|
|
```
|