cargo check

[root@bogon async]# cargo check
    Checking own v0.1.0 (/data2/rust/async)
error[E0670]: `async fn` is not permitted in the 2015 edition
 --> src/main.rs:6:1
  |
6 | async fn hello_world() {
  | ^^^^^ to use `async fn`, switch to Rust 2018
  |
  = help: set `edition = "2018"` in `Cargo.toml`
  = note: for more on editions, read https://doc.rust-lang.org/edition-guide

error[E0433]: failed to resolve: maybe a missing crate `futures`?
 --> src/main.rs:4:5
  |
4 | use futures::executor::block_on;
  |     ^^^^^^^ maybe a missing crate `futures`?

error[E0425]: cannot find function `block_on` in this scope
  --> src/main.rs:12:5
   |
12 |     block_on(future); // `future` is run and "hello, world!" is printed
   |     ^^^^^^^^ not found in this scope

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0425, E0433, E0670.
For more information about an error, try `rustc --explain E0425`.
error: could not compile `own`.

To learn more, run the command again with --verbose.
[root@bogon async]# 

 

cargo fmt

[root@bogon async]# cat Cargo.toml 
[package]

name = "own"
version = "0.1.0"
authors = ["Karthikeyan kartmuhil@gmail.com"]

[dependencies]
[root@bogon async]# cargo fmt
error[E0670]: `async fn` is not permitted in the 2015 edition
 --> /data2/rust/async/src/main.rs:6:1
  |
6 | async fn hello_world() {
  | ^^^^^ to use `async fn`, switch to Rust 2018
  |
  = help: set `edition = "2018"` in `Cargo.toml`
  = note: for more on editions, read https://doc.rust-lang.org/edition-guide

[root@bogon async]# cat Cargo.toml 
[package]

name = "own"
version = "0.1.0"
authors = ["Karthikeyan kartmuhil@gmail.com"]

[dependencies]

 

 

 

 

 cargo build
   Compiling own v0.1.0 (/data2/rust/async)
error[E0670]: `async fn` is not permitted in the 2015 edition
 --> src/main.rs:6:1
  |
6 | async fn hello_world() {
  | ^^^^^ to use `async fn`, switch to Rust 2018
  |
  = help: set `edition = "2018"` in `Cargo.toml`
  = note: for more on editions, read https://doc.rust-lang.org/edition-guide

error[E0433]: failed to resolve: maybe a missing crate `futures`?
 --> src/main.rs:4:5
  |
4 | use futures::executor::block_on;
  |     ^^^^^^^ maybe a missing crate `futures`?

error[E0425]: cannot find function `block_on` in this scope
  --> src/main.rs:12:5
   |
12 |     block_on(future); // `future` is run and "hello, world!" is printed
   |     ^^^^^^^^ not found in this scope

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0425, E0433, E0670.
For more information about an error, try `rustc --explain E0425`.
error: could not compile `own`.

To learn more, run the command again with --verbose.

 

 

 rustc -Vv
rustc 1.47.0 (18bf6b4f0 2020-10-07)
binary: rustc
commit-hash: 18bf6b4f01a6feaf7259ba7cdae58031af1b7b39
commit-date: 2020-10-07
host: aarch64-unknown-linux-gnu
release: 1.47.0
LLVM version: 11.0

 

 

我们要手工给项目对应的Cargo.toml添加edition = "2018"，试试cargo build，现在应该妥了。

cat Cargo.toml
[package]

name = "own"
version = "0.1.0"
authors = ["Karthikeyan kartmuhil@gmail.com"]
edition = "2018"
[dependencies]

 

cargo build
   Compiling own v0.1.0 (/data2/rust/async)
error[E0433]: failed to resolve: use of undeclared type or module `futures`
 --> src/main.rs:4:5
  |
4 | use futures::executor::block_on;
  |     ^^^^^^^ use of undeclared type or module `futures`

error[E0425]: cannot find function `block_on` in this scope
  --> src/main.rs:12:5
   |
12 |     block_on(future); // `future` is run and "hello, world!" is printed
   |     ^^^^^^^^ not found in this scope

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0425, E0433.
For more information about an error, try `rustc --explain E0425`.
error: could not compile `own`.

To learn more, run the command again with --verbose.

https://rust-lang.github.io/async-book/01_getting_started/04_async_await_primer.html
[dependencies]
futures = "0.3"

cat Cargo.toml 
[package]

name = "own"
version = "0.1.0"
authors = ["Karthikeyan kartmuhil@gmail.com"]
edition = "2018"
[dependencies]
futures = "0.3"

 

 cargo build
    Updating crates.io index
   Compiling proc-macro2 v1.0.24
   Compiling unicode-xid v0.2.1
   Compiling syn v1.0.55
   Compiling proc-macro-hack v0.5.19
   Compiling memchr v2.3.4
   Compiling proc-macro-nested v0.1.6
   Compiling futures-sink v0.3.8
   Compiling futures-core v0.3.8
   Compiling once_cell v1.5.2
   Compiling futures-io v0.3.8
   Compiling pin-utils v0.1.0
   Compiling slab v0.4.2
   Compiling futures-channel v0.3.8
   Compiling futures-task v0.3.8
   Compiling quote v1.0.8
   Compiling pin-project-internal v1.0.2
   Compiling futures-macro v0.3.8
   Compiling pin-project v1.0.2
   Compiling futures-util v0.3.8
   Compiling futures-executor v0.3.8
   Compiling futures v0.3.8
   Compiling own v0.1.0 (/data2/rust/async)
    Finished dev [unoptimized + debuginfo] target(s) in 40.35s
[root@bogon async]# cargo build
    Finished dev [unoptimized + debuginfo] target(s) in 0.03s
[root@bogon async]# cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.03s
     Running `target/debug/own`
hello, world!

 

// `block_on` blocks the current thread until the provided future has run to
// completion. Other executors provide more complex behavior, like scheudling
// multiple futures onto the same thread.
use futures::executor::block_on;

async fn hello_world() {
    println!("hello, world!");
}

fn main() {
    let future = hello_world(); // Nothing is printed
    block_on(future); // `future` is run and "hello, world!" is printed
}