171 lines
2.7 KiB
Markdown
171 lines
2.7 KiB
Markdown
# 引用和借用
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### 引用
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1. 🌟
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```rust,editable
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fn main() {
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let x = 5;
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// 填写空白处
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let p = __;
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println!("x 的内存地址是 {:p}", p); // output: 0x16fa3ac84
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}
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```
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2. 🌟
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```rust,editable
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fn main() {
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let x = 5;
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let y = &x;
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// 只能修改以下行
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assert_eq!(5, y);
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}
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```
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3. 🌟
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```rust,editable
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// 修复错误
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fn main() {
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let mut s = String::from("hello, ");
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borrow_object(s)
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}
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fn borrow_object(s: &String) {}
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```
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4. 🌟
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```rust,editable
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// 修复错误
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fn main() {
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let mut s = String::from("hello, ");
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push_str(s)
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}
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fn push_str(s: &mut String) {
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s.push_str("world")
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}
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```
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5. 🌟🌟
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```rust,editable
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fn main() {
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let mut s = String::from("hello, ");
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// 填写空白处，让代码工作
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let p = __;
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p.push_str("world");
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}
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```
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#### ref
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`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。
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6. 🌟🌟🌟
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```rust,editable
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fn main() {
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let c = '中';
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let r1 = &c;
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// 填写空白处，但是不要修改其它行的代码
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let __ r2 = c;
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assert_eq!(*r1, *r2);
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// 判断两个内存地址的字符串是否相等
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assert_eq!(get_addr(r1),get_addr(r2));
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}
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// 获取传入引用的内存地址的字符串形式
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fn get_addr(r: &char) -> String {
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format!("{:p}", r)
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}
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```
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### 借用规则
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7. 🌟
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```rust,editable
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// 移除代码某个部分，让它工作
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// 你不能移除整行的代码！
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fn main() {
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let mut s = String::from("hello");
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let r1 = &mut s;
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let r2 = &mut s;
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println!("{}, {}", r1, r2);
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}
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```
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#### 可变性
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8. 🌟 错误: 从不可变对象借用可变
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```rust,editable
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fn main() {
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// 通过修改下面一行代码来修复错误
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let s = String::from("hello, ");
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borrow_object(&mut s)
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}
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fn borrow_object(s: &mut String) {}
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```
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9. 🌟🌟 Ok: 从可变对象借用不可变
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```rust,editable
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// 下面的代码没有任何错误
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fn main() {
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let mut s = String::from("hello, ");
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borrow_object(&s);
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s.push_str("world");
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}
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fn borrow_object(s: &String) {}
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```
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### NLL
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10. 🌟🌟
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```rust,editable
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// 注释掉一行代码让它工作
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fn main() {
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let mut s = String::from("hello, ");
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let r1 = &mut s;
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r1.push_str("world");
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let r2 = &mut s;
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r2.push_str("!");
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println!("{}",r1);
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}
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```
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11. 🌟🌟
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```rust,editable
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fn main() {
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let mut s = String::from("hello, ");
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let r1 = &mut s;
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let r2 = &mut s;
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// 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
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// 你不能同时使用 r1 和 r2
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}
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```
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> 你可以在[这里](https://github.com/sunface/rust-by-practice/blob/master/solutions/ownership/borrowing.md)找到答案(在 solutions 路径下)
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