Ownership of Struct Data

简单引入生命周期概念

下列示例代码使用声明周期 'a 为 &str 这一引用类型,为 Rust编译器 提供了注解一样,避免了 User 结构体被 drop 时还对 username email形成悬垂引用的可能

// struct User {
//     username: &str, // !!! ERROR  编译器报错: expected named lifetime parameter
//     email: &str,    // !!! ERROR
//     sign_in_count: u64,
//     active: bool,
// }

struct User<'a> {
    username: &'a str,
    email: &'a str,
    sign_in_count: u64,
    active: bool,
}

fn main() {
    let _user = User {
        email: "yilonglei790@gmail.com",
        username: "etcetera",
        active: true,
        sign_in_count: 1,
    };
}

Struct Update

#[derive(Debug)]
struct Order {
    name: String,
    year: u32,
    made_by_phone: bool,
    made_by_mobile: bool,
    made_by_email: bool,
    item_number: u32,
    count: u32,
}

fn create_order_template() -> Order {
    Order {
        name: String::from("Bob"),
        year: 2019,
        made_by_phone: false,
        made_by_mobile: false,
        made_by_email: true,
        item_number: 123,
        count: 0,
    }
}

fn your_order() -> Order {
    let order_template = create_order_template();
    let your_order = Order {
        // 和 JavaScript 中结构覆盖一个道理,覆盖相同 key 的 value,
        // 下面练习代码新的 your_order 的 name、count 变为 “Hacker in Rust”, 1
        name: String::from("Hacker in Rust"),
        count: 1,
        ..order_template
    };
    return your_order;
}

fn main() {
    let x = your_order();
    println!("{:?}", x);
}

Struct with Methods

// 自动注入 Debug trait 方便格式化打印
#[derive(Debug)]
struct Package {
    sender_country: String,
    recipient_country: String,
    weight_in_grams: i32,
}

impl Package {
    // 第一个参数不为 self ｜ &self ｜ &mut self 情况下,该函数为关联函数,通过 Struct::func()调用,非关联函数使用Struct.func()调用
    fn new(sender_country: String, recipient_country: String, weight_in_grams: i32) -> Package {
        if weight_in_grams <= 0 {
            // This shouldn't happen so we panic
            panic!();
        }
        Package {
            // 强化语法,键值名称相同情况下可以用下面语法,和 JavaScript 中对象增强语法一个意思
            sender_country,
            recipient_country,
            weight_in_grams,
        }
    }

    fn is_international(&self) -> bool {
        self.sender_country != self.recipient_country
    }

    fn get_fees(&self, cents_per_gram: i32) -> i32 {
        self.weight_in_grams * cents_per_gram
    }
}

fn main() {
    let sender_country = String::from("Spain");
    let recipient_country = String::from("Germany");

    let package = Package::new(sender_country, recipient_country, 1200);

    if package.is_international() {
        println!(
            "{}",
            "The package from Spain to Germany is indeed international!"
        )
    } else {
        println!("{}", "Oops")
    }

    let sender_country = String::from("Spain");
    let recipient_country = sender_country.clone();

    let cents_per_gram = 3;

    let package = Package::new(sender_country, recipient_country, 1500);

    if !package.is_international() {
        println!(
            "{}",
            "The package from Spain to Spain is not international indeed!"
        )
    } else {
        println!("{}", "Oops")
    }

    let price = package.get_fees(cents_per_gram);
    println!("{}", "Your price is:");
    println!("{}", price);

    if package.get_fees(cents_per_gram) == 4500 {
        println!("{}", "The fees are correct!");
    } else {
        println!("{}", "The fees are wrong!")
    }
}