Rust系统编程之结构体

1.通用语法

1.1 声明

struct User {
    active: bool,
    username: String,
    email: String,
    sign_in_count: u64,
}

1.2 创建对象

常规写法

let user1 = User {
    email: String::from("someone@example.com"),
    username: String::from("someusername123"),
    active: true,
    sign_in_count: 1,
};

简化写法：参数如果名字一致，可以省略

fn build_user(email: String, username: String) -> User {
    User {
        email,
        username,
        active: true,
        sign_in_count: 1,
    }
}

1.3 拷贝

拷贝会发生所有权的转移

常规写法

let user2 = User {
    active: user1.active,
    username: user1.username,
    email: String::from("another@example.com"),
    sign_in_count: user1.sign_in_count,
};

简化写法

let user2 = User {
    email: String::from("another@example.com"),
    ..user1
};

2.特殊的结构体

2.1 元组结构体

当需要一个不关心名字的结构体时可以采用这种写法

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

let black = Color(0, 0, 0);
let origin = Point(0, 0, 0);

2.2 单元结构体

没有任何字段和属性的结构体

struct AlwaysEqual;

let subject = AlwaysEqual;

// 我们不关心 AlwaysEqual 的字段数据，只关心它的行为，因此将它声明为单元结构体，然后再为它实现某个特征
impl SomeTrait for AlwaysEqual {

}

3.含引用成员的结构体

// 标注生命周期
struct ImportantExcerpt<'a> {
    name: &'a str,
}

fn main() {
    let s = "test".to_string();
    let rs = &s;
    let i = ImportantExcerpt {
        name: rs,
    };
}

4.构造函数

不需要像C++一样必须和类名一致，参数不需要写Self。

impl Rectangle {
    fn square(size: u32) -> Self {
        Self {
            width: size,
            height: size,
        }
    }
}

5.成员函数

#[derive(Debug)]
struct Rectangle {
    width: u32,
    height: u32,
}

impl Rectangle {
    fn area(&self) -> u32 {
        self.width * self.height
    }
}

fn main() {
    let rect1 = Rectangle {
        width: 30,
        height: 50,
    };

    println!(
        "The area of the rectangle is {} square pixels.",
        rect1.area()
    );
}

4.格式化输出

#[derive(Debug)]使得结构体支持{:?}格式化输出

#[derive(Debug)]
struct Rectangle {
    width: u32,
    height: u32,
}

fn main() {
    let rect1 = Rectangle {
        width: 30,
        height: 50,
    };

    println!("rect1 is {:?}", rect1);
    // 更完整的调试信息输出宏
    dbg!(&rect1);
}

如果要支持{}格式化输出，需要实现Dispaly特征