Rust语言学习笔记（8）

OOP

实例 1

// src/lib.rs
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 Button {
    pub width: u32,
    pub height: u32,
    pub label: String,
}
impl Draw for Button {
    fn draw(&self) {
        // code to actually draw a button
    }
}

// src/main.rs
use gui::Draw;
use gui::{Screen, Button};
struct SelectBox {
    width: u32,
    height: u32,
    options: Vec<String>,
}
impl Draw for SelectBox {
    fn draw(&self) {
        // code to actually draw a select box
    }
}
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();
}

实例 2

// src/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());
}

// src/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
    }
}

实例 3

// src/lib.rs
pub struct Post {
    content: String,
}
pub struct DraftPost {
    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,
        }
    }
}
pub struct PendingReviewPost {
    content: String,
}
impl PendingReviewPost {
    pub fn approve(self) -> Post {
        Post {
            content: self.content,
        }
    }
}

// src/main.rs
use blog::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());
}