[Rust] Objects with Reference to Self and Lifetime Subtyping

[Rust] Objects with Reference to Self and Lifetime Subtyping.rs

use std::collections::HashMap;

type Handler<'a> = Box<dyn Fn(i32) -> i32 + 'a>;

pub struct Router<'r> {
	routes: HashMap<String, Handler<'r>>,
}

pub struct RouteAdder<'a, 'r: 'a> {
	router: &'a mut Router<'r>,
	route: String,
}

impl<'r> Router<'r> {
	pub fn new() -> Self {
		Router {
			routes: HashMap::new(),
		}
	}
	
	pub fn route<'a>(&'r mut self, route: String) -> RouteAdder<'a, 'r> {
		RouteAdder::of(self, route)
	}
	
	pub fn send(&self, s: &str, x: i32) -> Option<i32> {
		match self.routes.get(s) {
			None => None,
			Some(h) => Some(h(x)),
		}
	}
}

impl<'a, 'r> RouteAdder<'a, 'r> {
	fn of(router: &'a mut Router<'r>, route: String) -> Self {
		RouteAdder { router, route }
	}

	pub fn to(self, handler: impl Fn(i32) -> i32 + 'r) {
		self.router.routes.insert(self.route, Box::new(handler));
	}
}

#[cfg(test)]
mod tests {
	use super::*;

	#[test]
	fn test_route() {
		let router = {
			let mut router = Router::new();
			router.route(String::from("hello")).to(|x| x + 1);
			router
		};
		assert_eq!(router.send("hello", 3), Some(4));
	}
}

More detail: https://users.rust-lang.org/t/writing-fluent-code-creating-objects-with-reference-to-self-and-lifetime-subtyping/34130