[blog post] Nested method calls via two-phase borrowing

language design
20

Yeah, my playground link was something like that.

Actually, here's a much simpler example.

struct Something { mutex: Mutex<String> }
impl Something {
    fn one(&mut self) -> &str {
        self.mutex.get_mut().unwrap()
    }
    fn two(&self) {
        *self.mutex.lock().unwrap() = "Surprise!".to_owned();
    }
}

No unsafe code, fixed or invariant lifetimes, or structure returns, just (&mut self) -> &T, but calling two with the borrow from one still active would be Bad.

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