init code

4.Variable Bindings/4. Varable Bindings/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "veriable_bindings"
+version = "0.1.0"

4.Variable Bindings/4. Varable Bindings/Cargo.toml

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+[package]
+name = "veriable_bindings"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

4.Variable Bindings/4. Varable Bindings/src/main.rs

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+fn main() {
+    let an_integer = 1u32;
+    let a_boolean = true;
+    let unit = ();
+
+    // 储存在栈上的基础值，会直接复制
+    let copied_integer = an_integer;
+
+    println!("An integer: {:?}", copied_integer);
+    println!("A boolean: {:?}", a_boolean);
+    println!("Meet the unit value: {:?}", unit);
+
+    // 没有被使用的变量编译器会发出警告，可以通过在变量前面添加一个下划线来禁用编译器警告
+    let _unused_variable = 3u32;
+
+    let noisy_unused_variable = 2u32;
+    // FIXME ^ 在变量名前面添加下划线来禁用警告
+    // PS：网页的在线测试看不到警告信息
+}

4.Variable Bindings/4.1 Mutability/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "mutability"
+version = "0.1.0"

4.Variable Bindings/4.1 Mutability/Cargo.toml

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+[package]
+name = "mutability"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

4.Variable Bindings/4.1 Mutability/src/main.rs

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+fn main() {
+    let _immutable_binding = 1;
+    let mut mutable_binding = 1;
+
+    println!("Before mutation: {}", mutable_binding);
+
+    // 可变声明，所以可以修改
+    mutable_binding += 1;
+
+    println!("After mutation: {}", mutable_binding);
+
+    // 报错! 不可变声明不能修改内容
+    _immutable_binding += 1;
+}

4.Variable Bindings/4.2 Scope and Shadowing/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "scope_and_shadowing"
+version = "0.1.0"

4.Variable Bindings/4.2 Scope and Shadowing/Cargo.toml

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+[package]
+name = "scope_and_shadowing"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

4.Variable Bindings/4.2 Scope and Shadowing/src/main.rs

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+fn example01() {
+    // 在当前函数作用域中 绑定 1 到变量 long_lived_binding
+    let long_lived_binding = 1;
+
+    // 这个是一个内部嵌套的小范围作用域
+    {
+        // 这个变量声明只在当前的小范围内生效
+        let short_lived_binding = 2;
+
+        println!("inner short: {}", short_lived_binding);
+    }
+    // 嵌套的作用域结束，该作用域内的全部变量都会被回收
+
+    // 报错! `short_lived_binding` 这个变量已经被回收了
+    println!("outer short: {}", short_lived_binding);
+    // FIXME ^ 注释这行代码
+
+    println!("outer long: {}", long_lived_binding);
+}
+
+fn example02() {
+    let shadowed_binding = 1;
+
+    {
+        // 这里使用的变量值是外面的函数作用域的值
+        println!("before being shadowed: {}", shadowed_binding);
+
+        // 这里重新定义了一个同名的变量，进行了变量的遮蔽(shadowing)
+        let shadowed_binding = "abc";
+
+        println!("shadowed in inner block: {}", shadowed_binding);
+    }
+    // 小作用域已经结束，这里的变量使用的依旧是函数作用域的值
+    println!("outside inner block: {}", shadowed_binding);
+
+    // 这里对上面定义的变量重新定义，遮蔽（shadowing）了前面的变量声明
+    let shadowed_binding = 2;
+    println!("shadowed in outer block: {}", shadowed_binding);
+}
+
+fn main() {
+    example01();
+    example02();
+    println!("Hello, world!");
+}

4.Variable Bindings/4.3 Declare first/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "declare_first"
+version = "0.1.0"

4.Variable Bindings/4.3 Declare first/Cargo.toml

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+[package]
+name = "declare_first"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

4.Variable Bindings/4.3 Declare first/src/main.rs

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+//!
+//! 变量的定义和初始化通常是同时进行的。
+//! Rust 允许把两个操作分开，先定义，后初始化
+//! 使用变量的前提条件是变量必须被初始化了以后才能使用，否则在编译阶段就会报错
+//!
+//! 因为使用未初始化的变量通常会导致无法预知的行为，所以不允许使用未初始化的变量
+//!
+fn main() {
+    // 声明一个变量 但不对其进行初始化
+    let a_binding;
+
+    {
+        let x = 2;
+
+        // 初始化变量值
+        a_binding = x * x;
+    }
+
+    println!("a binding: {}", a_binding);
+
+    let another_binding;
+
+    // 报错! 使用了未初始化的变量
+    println!("another binding: {}", another_binding);
+    // FIXME ^ 注释这行代码
+
+    another_binding = 1;
+
+    println!("another binding: {}", another_binding);
+}

4.Variable Bindings/4.4 Freezing/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "freezing"
+version = "0.1.0"

4.Variable Bindings/4.4 Freezing/Cargo.toml

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+[package]
+name = "freezing"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

4.Variable Bindings/4.4 Freezing/src/main.rs

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+//!
+//! 可以通过使用子作用域遮蔽（shadowing）父作用域的同名可变变量成不可变变量
+//! 这样在这个子作用域内的同名变量就会是 冻结（Freezing）状态
+//! 直到子作用域结束
+//!
+fn main() {
+    let mut _mutable_integer = 7i32;
+
+    {
+        // 使用不可变遮蔽父作用域的同名变量
+        let _mutable_integer = _mutable_integer;
+
+        // 报错! 当前作用域中 `_mutable_integer` 变量是不可变的
+        _mutable_integer = 50;
+        // FIXME ^ 注释这行代码
+
+        // `_mutable_integer` 变量作用域结束
+    }
+
+    // `_mutable_integer` 这里可以修改，因为父作用域的定义是可变的
+    _mutable_integer = 3;
+}