future

问题 In flutter, I call a value from Firestore cloud database by using future and try to assigning this value to a variable. Here is my code: import 'package:cloud_firestore/cloud_firestore.dart'; import 'package:flutter/material.dart'; class Gyanpothro extends StatefulWidget { @override _GyanpothroState createState() => _GyanpothroState(); } class _GyanpothroState extends State<Gyanpothro> { Firestore db = Firestore.instance; Future databaseFuture; @override void initState() { databaseFuture = db

问题 In flutter, I call a value from Firestore cloud database by using future and try to assigning this value to a variable. Here is my code: import 'package:cloud_firestore/cloud_firestore.dart'; import 'package:flutter/material.dart'; class Gyanpothro extends StatefulWidget { @override _GyanpothroState createState() => _GyanpothroState(); } class _GyanpothroState extends State<Gyanpothro> { Firestore db = Firestore.instance; Future databaseFuture; @override void initState() { databaseFuture = db

问题 I would like to replicate the behavior and ergonomics of taking a closure/function as an argument much like map does: iterator.map(|x| ...) . I've noticed that some library code allows passing in async functionality, but this method doesn't allow me to pass in arguments: pub fn spawn<F, T>(future: F) -> JoinHandle<T> where F: Future<Output = T> + Send + 'static, T: Send + 'static, spawn(async { foo().await }); I'm hoping to do one of the following: iterator.map(async |x| {...}); async fn a(x:

问题 I would like to replicate the behavior and ergonomics of taking a closure/function as an argument much like map does: iterator.map(|x| ...) . I've noticed that some library code allows passing in async functionality, but this method doesn't allow me to pass in arguments: pub fn spawn<F, T>(future: F) -> JoinHandle<T> where F: Future<Output = T> + Send + 'static, T: Send + 'static, spawn(async { foo().await }); I'm hoping to do one of the following: iterator.map(async |x| {...}); async fn a(x:

问题 I would like to replicate the behavior and ergonomics of taking a closure/function as an argument much like map does: iterator.map(|x| ...) . I've noticed that some library code allows passing in async functionality, but this method doesn't allow me to pass in arguments: pub fn spawn<F, T>(future: F) -> JoinHandle<T> where F: Future<Output = T> + Send + 'static, T: Send + 'static, spawn(async { foo().await }); I'm hoping to do one of the following: iterator.map(async |x| {...}); async fn a(x:

问题 I would like to replicate the behavior and ergonomics of taking a closure/function as an argument much like map does: iterator.map(|x| ...) . I've noticed that some library code allows passing in async functionality, but this method doesn't allow me to pass in arguments: pub fn spawn<F, T>(future: F) -> JoinHandle<T> where F: Future<Output = T> + Send + 'static, T: Send + 'static, spawn(async { foo().await }); I'm hoping to do one of the following: iterator.map(async |x| {...}); async fn a(x:

问题 use futures::{future, Future}; fn test() -> Box<dyn Future<Output = bool>> { Box::new(future::ok::<bool>(true)) } async fn async_fn() -> bool { let result: bool = test().await; return result; } fn main(){ async_fn(); println!("Hello!"); } Playground Error: error[E0277]: the trait bound `dyn core::future::future::Future<Output = bool>: std::marker::Unpin` is not satisfied --> src/main.rs:8:24 | 8 | let result: bool = test().await; | ^^^^^^^^^^^^ the trait `std::marker::Unpin` is not

问题 I'd like to be able to sleep my future for a single "frame" so that other work can happen. Is this a valid implementation of this idea? use std::future::Future; use std::task::{Context, Poll}; use std::pin::Pin; struct Yield { yielded: bool, } impl Future for Yield { type Output = (); fn poll(mut self: Pin<&mut Self>, ctx: &mut Context) -> Poll<()> { if self.yielded { Poll::Ready(()) } else { self.yielded = true; // This is the part I'm concerned about ctx.waker().wake_by_ref(); Poll::Pending

问题 I am attempting to create simplest possible example that can get async fn hello() to eventually print out Hello World! . This should happen without any external dependency like tokio , just plain Rust and std . Bonus points if we can get it done without ever using unsafe . #![feature(async_await)] async fn hello() { println!("Hello, World!"); } fn main() { let task = hello(); // Something beautiful happens here, and `Hello, World!` is printed on screen. } I know async/await is still a nightly

问题 I am attempting to create simplest possible example that can get async fn hello() to eventually print out Hello World! . This should happen without any external dependency like tokio , just plain Rust and std . Bonus points if we can get it done without ever using unsafe . #![feature(async_await)] async fn hello() { println!("Hello, World!"); } fn main() { let task = hello(); // Something beautiful happens here, and `Hello, World!` is printed on screen. } I know async/await is still a nightly