Спостерігач на Rust
Спостерігач — це поведінковий патерн, який дозволяє об’єктам повідомляти інші об’єкти про зміни свого стану.
При цьому спостерігачі можуть вільно підписуватися і відписуватись від цих повідомлень.
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
