How tokio join macro works

tokio's join macro is pretty amazing

https://docs.rs/tokio/0.2.20/tokio/macro.join.html

To find out how this join! macro works exactly,  you can do blow to expand the macro to see exact code generated.

rustup toolchain install nightly
cargo install cargo-expand

then in your project

cargo expand

You will find the expanded code like below

	// Macro expaned from
	// let (first, second) = tokio::join!(do_stuff1(), do_stuff2());
	let (first, second) = {
	use ::tokio::macros::support::{maybe_done, poll_fn, Future, Pin};
	use ::tokio::macros::support::Poll::{Ready, Pending};
	let mut futures = (maybe_done(do_stuff1()), maybe_done(do_stuff2()));
	poll_fn(move |cx| {
	let mut is_pending = false;
	let (fut, ..) = &mut futures;
	let mut fut = unsafe { Pin::new_unchecked(fut) };
	if fut.poll(cx).is_pending() {
	is_pending = true;
	}
	let (_, fut, ..) = &mut futures;
	let mut fut = unsafe { Pin::new_unchecked(fut) };
	if fut.poll(cx).is_pending() {
	is_pending = true;
	}
	if is_pending {
	Pending
	} else {
	Ready((
	{
	let (fut, ..) = &mut futures;
	let mut fut = unsafe { Pin::new_unchecked(fut) };
	fut.take_output().expect("expected completed future")
	},
	{
	let (_, fut, ..) = &mut futures;
	let mut fut = unsafe { Pin::new_unchecked(fut) };
	fut.take_output().expect("expected completed future")
	},
	))
	}
	})
	.await
	};

view raw tokio_join_expand.rs hosted with ❤ by GitHub

Usage of serde_json

Some sample code shows behavior of serde_json.

I used to write code like

val.as_object().unwrap().get("field_name").unwrap().as_object().unwrap().get_("sub_field_name").as_str().unwrap().

Turns out that using index of serde_json makes code much less verbose.

	use serde_json::Value;
	fn main() {
	let test_json = r#"
	{
	"a":"a_val",
	"b":{
	"b_sub" : "b_sub_val"
	},
	"d":[
	{
	"d0" : "d0_val"
	},
	{
	"d1" : "d1_val"
	}
	]
	}
	"#;
	let val: Value = serde_json::from_str(test_json).unwrap();
	println!("{}", val["a"]);
	println!("{}", val["b"]);
	println!("{}", val["b"]["b_sub"]);
	println!("{}", val["b"]["b_sub"].to_string());
	println!("{}", val["b"]["b_sub"].as_str().unwrap());
	println!("{}", val["d"][0]["d0"].as_str().unwrap());
	println!("{}", val["no_exist"]["what_will_happen"]);
	}

view raw playground.rs hosted with ❤ by GitHub