Rust 结构体 (struct) 的详细知识点

struct User {
    name: String,
    age: u32,
    is_vip: bool,
}

// 实例化
let u = User {
    name: "张三".to_string(),
    age: 22,
    is_vip: false,
};

// 访问/修改（必须 mut 实例）
println!("{}", u.name);
let mut u2 = User { name: "李四".into(), age: 30, is_vip: true };
u2.age = 31;

struct Point(i32, i32);
struct Color(u8, u8, u8);

let p = Point(10, 20);
println!("{} {}", p.0, p.1);

struct EmptyFlag;
let flag = EmptyFlag;

fn build_user(name: String, age: u32) -> User {
    User {
        name,  // 等价 name: name
        age,
        is_vip: false,
    }
}

let u1 = User { name: "A".into(), age: 18, is_vip: false };
let u2 = User { age: 20, ..u1 };
// u2.name = "A", u2.is_vip = false，仅 age 改为 20

struct Point { x: i32, y: f64 }
let p = Point {x:1, y:2.0}; // 全部栈

struct Student {
    id: u64,
    name: String,   // String 栈存三元指针，字符堆
    scores: Vec<u8> // Vec 栈存指针数组，元素堆
}
let s = Student { ... };
// s 整体在栈；name、scores 的真实数据在堆

let heap_point: Box<Point> = Box::new(Point{x:0, y:0});
// heap_point 变量栈；Point 结构体存在堆

#[repr(C)]
struct CPoint {
    x: i32,
    y: i32,
}

impl User {
    // 构造器，关联函数
    fn new(name: &str, age: u32) -> Self {
        Self {
            name: name.to_string(),
            age,
            is_vip: false,
        }
    }
}
let u = User::new("老王", 25);

impl User {
    // 只读方法
    fn get_age(&self) -> u32 {
        self.age
    }
    // 修改自身
    fn become_vip(&mut self) {
        self.is_vip = true;
    }
    // 拿走所有权
    fn consume(self) {
        println!("{}", self.name);
    }
}

impl User {
    const MAX_AGE: u32 = 150;
}
println!("{}", User::MAX_AGE);

let User { name, age, is_vip } = u;
// name 拿到 String 所有权，u 失效

let User { ref name, .. } = &u;
// 等价 let name = &u.name;

let mut u = User::new("test", 20);
let a = &u.name; // 不可变借用
let b = &mut u.age; // 可变借用
// 同一字段不能同时存在可变 + 不可变借用；不同字段允许

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct Point { x: i32, y: i32 }

struct Address {
    city: String,
    street: String,
}

struct User {
    name: String,
    addr: Address, // 嵌套结构体
}

// 访问
user.addr.city

// 报错：无限大小
struct Node {
    next: Node
}

// 正确，Box 栈存指针，子节点堆分配
struct Node {
    val: i32,
    next: Option<Box<Node>>
}