typestate_in_rust.rs

use std::sync::Arc;

type Log = Box<dyn Fn(&str)>;

struct OpenLibrary {
	pub log: Log,
}

struct OpenDevice {
	library: Arc<OpenLibrary>,
}

impl OpenLibrary {
	pub fn new(log: Log) -> Arc<OpenLibrary> {
		log("Open library");
		Arc::new(OpenLibrary { log })
	}

	pub fn do_use(&self) {
		(self.log)("  Use library");
	}

	pub fn open_device(self: Arc<Self>) -> OpenDevice {
		OpenDevice::new(self.clone())
	}
}

impl Drop for OpenLibrary {
	fn drop(&mut self) {
		(self.log)("Close library");
	}
}

impl OpenDevice {
	fn new(library: Arc<OpenLibrary>) -> OpenDevice {
		(library.log)("  Open device");
		OpenDevice { library }
	}

	pub fn do_use(&self) {
		(self.library.log)("    Use device");
	}

	pub fn close(self) -> Arc<OpenLibrary> {
		self.library.clone()
	}
}

impl Drop for OpenDevice {
	fn drop(&mut self) {
		(self.library.log)("  Close device");
	}
}

fn main() {
	let log = |s: &str| { println!("{}", s) };

	{ // Case 1: Lib -> Dev -> Done
		let lib = OpenLibrary::new(Box::new(log));
		lib.do_use();
		let dev = lib.open_device();
		dev.do_use();
	}

	{ // Case 2: Lib -> Dev -> Lib -> Done
		let lib = OpenLibrary::new(Box::new(log));
		lib.do_use();
		let dev = lib.open_device();
		dev.do_use();
		let lib = dev.close();
		lib.do_use();
	}
}