Code shared from the Rust Playground

playground.rs

#[derive(Debug)]
struct Hoge {
    id: usize,
    ok: bool,
}

impl Drop for Hoge {
    fn drop(&mut self) {
        assert!(self.ok, "must call .ok() (id: {})", self.id);
    }
}

impl Hoge {
    fn new(id: usize) -> Self {
        Self { id, ok: false }
    }
    fn next(mut self, check: i32) -> Result<Self, ()> {
        self.ok = true;
        if check < 10 {
            Ok(Self {
                id: self.id,
                ok: false,
            })
        } else {
            Err(())
        }
    }
    fn ok(mut self, check: i32) -> Result<(), ()> {
        self.ok = true;
        if check < 10 {
            Ok(())
        } else {
            Err(())
        }
    }
}

pub fn run() -> Result<(), ()> {
    let h0 = Hoge::new(0);
    let h1 = Hoge::new(1);
    let h2 = Hoge::new(3);
    let h3 = Hoge::new(4);

    h0.next(3)?;
    h1.next(4)?.next(9)?.ok(3)?;
    h2.next(10)?.next(4)?.ok(3)?;
    h3.ok(4)?;

    Ok(())
}

#[cfg(test)]
mod test {
    #[test]
    fn it_works() {
        super::run().unwrap();
    }
}