Rust 观察者模式讲解和代码示例
观察者是一种行为设计模式， 允许一个对象将其状态的改变通知其他对象
观察者模式提供了一种作用于任何实现了订阅者接口的对象的机制， 可对其事件进行订阅和取消订阅。
Conceptual example
In Rust, a convenient way to define a subscriber is to have a function as a callable object with complex logic passing it to a event publisher.
In this Observer example, Subscribers are either a lambda function or an explicit function subscribed to the event. Explicit function objects could be also unsubscribed (although, there could be limitations for some function types).
editor.rs
use crate::observer::{Event, Publisher}; /// Editor has its own logic and it utilizes a publisher /// to operate with subscribers and events. #[derive(Default)] pub struct Editor { publisher: Publisher, file_path: String, } impl Editor { pub fn events(&mut self) -> &mut Publisher { &mut self.publisher } pub fn load(&mut self, path: String) { self.file_path = path.clone(); self.publisher.notify(Event::Load, path); } pub fn save(&self) { self.publisher.notify(Event::Save, self.file_path.clone()); } } observer.rs
use std::collections::HashMap; /// An event type. #[derive(PartialEq, Eq, Hash, Clone)] pub enum Event { Load, Save, } /// A subscriber (listener) has type of a callable function. pub type Subscriber = fn(file_path: String); /// Publisher sends events to subscribers (listeners). #[derive(Default)] pub struct Publisher { events: HashMap<Event, Vec<Subscriber>>, } impl Publisher { pub fn subscribe(&mut self, event_type: Event, listener: Subscriber) { self.events.entry(event_type.clone()).or_default(); self.events.get_mut(&event_type).unwrap().push(listener); } pub fn unsubscribe(&mut self, event_type: Event, listener: Subscriber) { self.events .get_mut(&event_type) .unwrap() .retain(|&x| x != listener); } pub fn notify(&self, event_type: Event, file_path: String) { let listeners = self.events.get(&event_type).unwrap(); for listener in listeners { listener(file_path.clone()); } } } main.rs
use editor::Editor; use observer::Event; mod editor; mod observer; fn main() { let mut editor = Editor::default(); editor.events().subscribe(Event::Load, |file_path| { let log = "/path/to/log/file.txt".to_string(); println!("Save log to {}: Load file {}", log, file_path); }); editor.events().subscribe(Event::Save, save_listener); editor.load("test1.txt".into()); editor.load("test2.txt".into()); editor.save(); editor.events().unsubscribe(Event::Save, save_listener); editor.save(); } fn save_listener(file_path: String) { let email = "admin@example.com".to_string(); println!("Email to {}: Save file {}", email, file_path); } Output
Save log to /path/to/log/file.txt: Load file test1.txt Save log to /path/to/log/file.txt: Load file test2.txt Email to admin@example.com: Save file test2.txt
