async_fut_exp_in_200_lines_5_gen.rs

// books-futures-explained
// https://cfsamson.github.io/books-futures-explained/4_generators_async_await.html

#![feature(generators, generator_trait)]
use std::ops::{Generator, GeneratorState};

fn main() {
    let a: i32 = 4;
    let mut gen = move || {
        println!("Hello");
        yield a * 2;
        println!("world");
    };

    if let GeneratorState::Yielded(n) =
        gen.resume() { println!("Got value {}", n); }
    if let GeneratorState::Complete(()) = gen.resume() { println!("Complete"); }

    let mut generator = move || {
        let to_borrow = String::from("Hello");
        let borrowed = &to_borrow;
        yield borrowed.len();
        println!("{} world!", borrowed);
    };


#![allow(unused)]
fn main() {
enum GeneratorState<Y, R> {
    Yielded(Y),
    Complete(R),
}

trait Generator {
    type Yield;
    type Return;
    fn resume(&mut self) -> GeneratorState<Self::Yield, Self::Return>;
}

enum GeneratorA {
    Enter,
    Yield1 {
        to_borrow: String,
        borrowed: &String, // uh, what lifetime should this have?
    },
    Exit,
}

impl GeneratorA {
    fn start() -> Self {
        GeneratorA::Enter
    }
}

impl Generator for GeneratorA {
    type Yield = usize;
    type Return = ();
    fn resume(&mut self) -> GeneratorState<Self::Yield, Self::Return> {
        // lets us get ownership over current state
        match std::mem::replace(self, GeneratorA::Exit) {
            GeneratorA::Enter => {
                let to_borrow = String::from("Hello");
                let borrowed = &to_borrow; // <--- NB!
                let res = borrowed.len();

                *self = GeneratorA::Yield1 {to_borrow, borrowed};
                GeneratorState::Yielded(res)
            }

            GeneratorA::Yield1 {to_borrow, borrowed} => {
                println!("Hello {}", borrowed);
                *self = GeneratorA::Exit;
                GeneratorState::Complete(())
            }
            GeneratorA::Exit => panic!("Can't advance an exited generator!"),
        }
    }
}
}










}