Day 20: Know Your Status

“IS THE SLEIGH PARKED, READY, OR FLYING? WHY DOESN’T ANYONE KNOW?”

“Uh… shouldn’t you know? Didn't we use the type state pattern?” Bernard spoke up.

Santa's face twitched. "Of course, we used the type state pattern! But does anyone have a quick way to check the state right now? There are some sleighs in the air, it's hard to keep track on all of them."

Blitzen, lounging in a corner, snorted. “Sounds like y'all need to add a status() method.”

Prancer’s ears perked up. “Yeah! A single method we can call to figure out the state, no matter which one it’s in.”

Santa stroked his beard, muttering. “Fine. Add it. And make sure it’s compile-time safe. If I get a wrong answer, someone’s spending Christmas hand-delivering packets in binary.”

Your Mission

It's time to give Santa what he wants: a single status() method that works in all states of the sleigh (Empty, Ready, and Flying), returning the current state as a string.

Here's the plan:

  1. Define the status() method: It should be callable on the Sleigh regardless of its state.
  2. Return a string indicating the sleigh’s state:
    • "Empty" when the sleigh is empty.
    • "Ready" when the sleigh is loaded and ready to fly.
    • "Flying" when the sleigh is in the air.
  3. The Sleigh struct should have a trait bound, not just a generic <T>.

Here's how Santa wants to the the API:

let sleigh = Sleigh::new();
assert_eq!(sleigh.status(), "Empty");
 
sleigh.load();
assert_eq!(sleigh.status(), "Ready");
 
sleigh.take_off();
assert_eq!(sleigh.status(), "Flying");

Hints

If you’re unsure where to start, take a look at these tips:

Click to reveal hints!

  • Use a trait to define shared behavior across all states. For example:

    pub trait State {
    fn status() -> &'static str;
}

  • Implement the trait for each state. e.g.

    impl State for Empty {
    fn status() -> &'static str {
        "Empty"
    }
}

  • Implement a method for all types that implement the State trait. e.g.

    impl<T: State> Sleigh<T> {
  pub fn status(&self) -> &'static str {
      T::status()
  }
}