rust 变量基础

变量绑定基础概念

fn main() {

    let x = 5; 
    let (m, n) = (1, 2);    // 等号左侧是一个 “模式” 
    println!("m => {} ; n => {}; ", m, n);

    // 类型注解，无注解编译器 类型推断
    let y: i32 = 5;     // i开头有符号
    let k: u32 = 10;    // u开头无符号

    // 可变性 (Mutability)
    // 绑定默认是不可变的(immutable)
    let v1 = 5;
    // v1 = 10;         // 编译出错 提示：re-assignment of immutable variable
    let mut v2 = 5;
    v2 = 10;            // mut 绑定可以赋值
    println!("v2 value : {}", v2);

    // 初始化绑定
    let v3: i32;        // 未赋值不允许使用
    // println!("v3 value : {}", v3);   编译提示：re-assignment of immutable variable

    // 作用域和隐藏
    let v4: i32 = 17;
    {
        let v5: i32 = 3;
        println!("v4, v5 value: {}, {}", v4, v5);
    }
    // cannot find value `v5` in this scope
    // println!("v4, v5 value: {}, {}", v4, v5);    
    let v6: i32 = 8;
    {
        println!("v6 value: {}", v6); // 8
        let v6: i32 = 12;
        println!("v6 value: {}", v6); // 12  被 let v6: i32 = 12; 隐藏了
    }
    println!("v6 value: {}", v6);     // 8   恢复
}