2022-02-24 01:50:01 -06:00
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# 变量绑定与解构
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### 绑定和可变性
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🌟 修复下面代码的错误并尽可能少的修改
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```rust,editable
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fn main() {
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let x: i32; // 未初始化,但被使用
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let y: i32; // 未初始化,也未被使用
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println!("{} is equal to 5", x);
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}
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```
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🌟🌟 完形填空,让代码编译
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```rust,editable
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fn main() {
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// 使用合适的变量名替代 __
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let __ = 1;
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__ += 2;
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println!("{} = 3", x);
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}
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```
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### 变量作用域
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🌟 修复下面代码的错误并使用尽可能少的改变
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```rust,editable
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fn main() {
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let x: i32 = 10;
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{
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let y: i32 = 5;
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println!("x 的值是 {}, y 的值是 {}", x, y);
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}
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println!("x 的值是 {}, y 的值是 {}", x, y);
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}
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```
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🌟🌟 使用你所掌握的知识来修复错误
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```rust,editable
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fn main() {
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println!("{}, world", x);
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}
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fn define_x() {
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let x = "hello";
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}
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```
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### 变量遮蔽( Shadowing )
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🌟🌟 只允许修改 `assert_eq!` 来让 `println!` 工作(在终端输出 `42`)
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```rust,editable
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fn main() {
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let x: i32 = 5;
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{
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let x = 12;
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assert_eq!(x, 5);
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}
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assert_eq!(x, 12);
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let x = 42;
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println!("{}", x); // 输出 "42".
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}
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```
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🌟🌟 删除一行代码以通过编译
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```rust,editable
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fn main() {
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let mut x: i32 = 1;
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x = 7;
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// 遮蔽且再次绑定
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let x = x;
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x += 3;
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let y = 4;
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// 遮蔽
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let y = "I can also be bound to text!";
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}
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```
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### 未使用的变量
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使用以下方法来修复编译器输出的 warning :
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- 🌟 一种方法
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- 🌟🌟 两种方法
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> 注意: 你可以使用两种方法解决,但是它们没有一种是移除 `let x = 1` 所在的代码行
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```rust,editable
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fn main() {
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let x = 1;
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}
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// compiler warning: unused variable: `x`
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```
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### 变量解构
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🌟🌟 修复下面代码的错误并尽可能少的修改
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> 提示: 可以使用变量遮蔽或可变性
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```rust,editable
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fn main() {
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let (x, y) = (1, 2);
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x += 2;
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assert_eq!(x, 3);
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assert_eq!(y, 2);
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}
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```
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