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我尝试从Heads-up Design Patterns 中实现观察者模式，它最初是用 Java 编写的：

use std::cell::RefCell;
use std::rc::Rc;
use std::borrow::BorrowMut;

trait Subject {
    fn registerObserver(&mut self, observer: Rc<RefCell<Observer>>);
    fn removeObserver(&mut self, observer: Rc<RefCell<Observer>>);
    fn notifyObserver(&self, observer: Rc<RefCell<Observer>>);
}

trait Observer {
    fn update(&mut self, data: f32);
}


struct Teacher {
    observers: Vec<Rc<RefCell<Observer>>>,
    data: f32,
}
impl Teacher {
    pub fn print(&self) {
        println!("teacher = {:}", self.data);
    }
}
impl Subject for Teacher {
    fn registerObserver(&mut self, observer: Rc<RefCell<Observer>>) {
        self.observers.push(observer);
    }
    fn removeObserver(&mut self, …