《Rust权威指南》第17章_Rust的面向对象编程特性_草稿

• 面向对象语言的特性
  • 对象包含数据和行为
  • 封装实现细节
  • 作为类型系统和代码共享机制的继承
• 使用trait对象来存储不同类型的值
  • 为共有行为定义一个trait
  • 实现trait
  • trait对象会执行动态派发
  • trait对象必须保证对象安全
• 实现一种面向对象的设计模式
  • 定义Post并新建一个处于草稿状态下的新实例
  • 存储文章内容的文本
  • 确保草稿的可读内容为空
  • 请求审批文章并改变其状态
  • 添加approve方法来改变content的行为
  • 状态模式的权衡取舍
    • 将状态和行为编码成类型

OOP

main.rs:

use OOP::{Screen, Button, SelectBox};

fn main() {
    let screen = Screen {
        components: vec![
            Box::new(SelectBox{
                width: 75,
                height: 10,
                options: vec![
                    String::from("Yes"),
                    String::from("Maybe"),
                    String::from("No"),
                ],
            }),
            Box::new(Button {
                width: 50,
                height: 10,
                label: String::from("OK"),
            })
        ],
    };

    screen.run();
}

lib.rs:

pub struct AveragedCollection {
    list: Vec<i32>,
    average: f64,
}

impl AveragedCollection {
    pub fn add(&mut self, value: i32) {
        self.list.push(value);
        self.update_average();
    }

    pub fn remove(&mut self) -> Option<i32> {
        let result = self.list.pop();
        match result {
            Some(value) => {
                self.update_average();
                Some(value)
            },
            None => None,
        }
    }

    pub fn average(&self) -> f64 {
        self.average
    }

    fn update_average(&mut self) {
        let total: i32 = self.list.iter().sum();
        self.average = total as f64 / self.list.len() as f64;
    }
}

pub trait Draw {
    fn draw(&self);
}

pub struct Screen {
    pub components: Vec<Box<dyn Draw>>,
}

impl Screen {
    pub fn run(&self) {
        for component in self.components.iter() {
            component.draw();
        }
    }
}

/*
pub struct Screen {
    pub components: Vec,
}

impl Screen
    where T: Draw{
    pub fn run(&self) {
        for component in self.components.iter() {
            component.draw();
        }
    }
}
 */

pub struct Button {
    pub width: u32,
    pub height: u32,
    pub label: String,
}

impl Draw for Button {
    fn draw(&self) {
        // 实际绘制一个按钮的代码
    }
}

pub struct SelectBox {
    pub width: u32,
    pub height: u32,
    pub options: Vec<String>,
}

impl Draw for SelectBox {
    fn draw(&self) {
        // 实际绘制一个选择框的代码
    }
}

post

main.rs:

use blog::Post;

fn main() {
    let mut post = Post::new();

    post.add_text("I ate a salad for lunch today");
    assert_eq!("",post.content());

    post.request_review();
    assert_eq!("", post.content());

    post.approve();
    assert_eq!("I ate a salad for lunch today", post.content());
}

lib.rs:

pub struct Post {
    state: Option<Box<dyn State>>,
    content: String,
}

impl Post {
    pub fn new() -> Post {
        Post {
            state: Some(Box::new(Draft {})),
            content: String::new(),
        }
    }

    pub fn add_text(&mut self, text: &str) {
        self.content.push_str(text);
    }

    pub fn content(&self) -> &str {
        self.state.as_ref().unwrap().content(&self)
    }

    pub fn request_review(&mut self) {
        if let Some(s) = self.state.take() {
            self.state = Some(s.request_review())
        }
    }
    
    pub fn approve(&mut self) {
        if let Some(s) = self.state.take() {
            self.state = Some(s.approve());
        }
    }
}

trait State {
    fn request_review(self: Box<Self>) -> Box<dyn State>;
    fn approve(self: Box<Self>) -> Box<dyn State>;
    fn content<'a>(&self, post: &'a Post) -> &'a str {
        ""
    }
}

struct Draft {

}

impl State for Draft {
    fn request_review(self: Box<Self>) -> Box<dyn State> {
        Box::new(PendingReview {})
    }

    fn approve(self: Box<Self>) -> Box<dyn State> {
        self
    }
}

struct PendingReview {}

impl State for PendingReview {
    fn request_review(self: Box<Self>) -> Box<dyn State> {
        self
    }

    fn approve(self: Box<Self>) -> Box<dyn State> {
        Box::new(Published {})
    }
}

struct Published {}

impl State for Published {
    fn request_review(self: Box<Self>) -> Box<dyn State> {
        self
    }

    fn approve(self: Box<Self>) -> Box<dyn State> {
        self
    }

    fn content<'a>(&self, post: &'a Post) -> &'a str {
        &post.content
    }
}

post_2

main.rs:

use blog_2::Post;

fn main() {
    let mut post = Post::new();

    post.add_text("I ate a salad for lunch today");

    let post = post.request_review();

    let post = post.approve();

    assert_eq!("I ate a salad for lunch today", post.content());
}

lib.rs:

pub struct Post {
    content: String,
}

pub struct DraftPost {
    content: String,
}

pub struct PendingReviewPost {
    content: String,
}

impl Post {
    pub fn new() -> DraftPost {
        DraftPost {
            content: String::new(),
        }
    }

    pub fn content(&self) -> &str {
        &self.content
    }
}

impl DraftPost {
    pub fn add_text(&mut self, text: &str) {
        self.content.push_str(text);
    }

    pub fn request_review(self) -> PendingReviewPost {
        PendingReviewPost {
            content: self.content,
        }
    }
}

impl PendingReviewPost {
    pub fn approve(self) -> Post {
        Post {
            content: self.content,
        }
    }
}