Async Enums

Enums สำหรับ async programming

Poll

use std::task::Poll;
use std::future::Future;
use std::pin::Pin;
use std::task::Context;

// Poll is the core of Future
enum ExamplePoll<T> {
    Ready(T),    // Value is ready
    Pending,     // Not ready yet, will wake
}

// Custom future
struct CountDown {
    remaining: u32,
}

impl Future for CountDown {
    type Output = &'static str;

    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
        if self.remaining == 0 {
            Poll::Ready("Done!")
        } else {
            self.remaining -= 1;
            // In real code: schedule wake-up
            // cx.waker().wake_by_ref();
            Poll::Pending
        }
    }
}

fn main() {
    // Poll variants
    let ready: Poll<i32> = Poll::Ready(42);
    let pending: Poll<i32> = Poll::Pending;

    // Check status
    println!("ready.is_ready(): {}", ready.is_ready());
    println!("pending.is_pending(): {}", pending.is_pending());

    // Map the value
    let mapped = ready.map(|x| x * 2);
    println!("Mapped: {:?}", mapped);

    // Poll methods
    if let Poll::Ready(value) = ready {
        println!("Value: {}", value);
    }
}