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//!

//! http://doc.rust-lang.org/complement-cheatsheet.html#how-do-i-express-phantom-types?

use std::marker::PhantomData;

// Phantom types are useful for enforcing state at compile time. For example:

struct Door<State>(String, PhantomData<State>);

struct Open;

struct Closed;

fn close(door: Door<Open>) -> Door<Closed> {

let name = door.0;

println!("The door '{}' is closed.", name);

Door::<Closed>(name, PhantomData)

}

fn open(door: Door<Closed>) -> Door<Open> {

let name = door.0;

println!("The door '{}' is open.", name);

Door::<Open>(name, PhantomData)

}

/*

fn do_not_compile() {

// Attempting to close a closed door is prevented statically:

let _ = close(Door::<Closed>("front", PhantomData)); // error: mismatched types: expected `Door<Open>`, found `Door<Closed>`

}

*/

#[cfg(not(test))]

fn main() {

let opened_front_door = Door::<Open>("front".to_string(), PhantomData);

let closed_front_door = close(opened_front_door);

let _ = open(closed_front_door);

}