very clever rust developer

main.rs

#![allow(dead_code)]
use std::fmt::{Display, Formatter};

struct Sad;
struct Happy;

#[derive(Debug)]
enum RustLevel {
    Beginner,
    TrashDevLevel,
    Intermediate,
    DonutLevel,
}

impl Display for RustLevel {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        match self {
            RustLevel::Beginner => write!(f, "beginner"),
            RustLevel::TrashDevLevel => write!(f, "trash dev level"),
            RustLevel::Intermediate => write!(f, "intermediate"),
            RustLevel::DonutLevel => write!(f, "donut level"),
        }
    }
}

struct Barry<LifeState = Happy> {
    rust_level: RustLevel,
    life_state: std::marker::PhantomData<LifeState>,
}

impl Barry {
    pub fn new() -> Self {
        Barry {
            rust_level: RustLevel::Beginner,
            life_state: std::marker::PhantomData::<Happy>,
        }
    }
}

impl<LifeState> Barry<LifeState> {
    pub fn say_hello(&self) {
        println!("Hello am Barry am a {} rust developer", self.rust_level);
    }

    pub fn advance_rust_level(&mut self) {
        self.rust_level = match self.rust_level {
            RustLevel::Beginner => RustLevel::Intermediate,
            RustLevel::Intermediate => RustLevel::DonutLevel,
            RustLevel::DonutLevel => RustLevel::TrashDevLevel,
            RustLevel::TrashDevLevel => RustLevel::TrashDevLevel,
        }
    }
}

impl Barry<Sad> {
    pub fn cry(&self) {
        println!("barry cry now, no job... no trash livestrem...");
    }

    pub fn get_job(self) -> Barry<Happy> {
        Barry {
            rust_level: self.rust_level,
            life_state: std::marker::PhantomData::<Happy>,
        }
    }
}

impl Barry<Happy> {
    pub fn dance(&self) {
        println!("barry dance now, baby shark duh duh duh duh duh duh");
    }

    pub fn go_homeless(self) -> Barry<Sad> {
        Barry {
            rust_level: self.rust_level,
            life_state: std::marker::PhantomData::<Sad>,
        }
    }
}

fn main() {
    let barry = Barry::new();
    barry.say_hello();
    barry.dance();
    let barry = barry.go_homeless();
    barry.say_hello();
    barry.cry();
    let mut barry = barry.get_job();
    barry.advance_rust_level();
    barry.say_hello();
    barry.dance();
}