# Implementation of the `union!` macro.
# `union!`
`union!` - one macro to rule them all. Provides useful shortcut combinators, combines sync/async chains, transforms tuple of results in result of tuple, supports single and multi thread (sync/async) step by step execution of branches.
Using this macro you can write things like
```rust no_run
#![recursion_limit="1024"]
use union::union_async;
use futures::stream::{iter, Stream};
use reqwest::Client;
use futures::future::{try_join_all, ok, ready};
use failure::{format_err, Error};
fn get_urls_to_calculate_link_count() -> impl Stream<Item = &'static str> {
iter(
vec![
"https://en.wikipedia.org/w/api.php?format=json&action=query&generator=random&grnnamespace=0&prop=revisions|images&rvprop=content&grnlimit=100",
"https://github.com/explore",
"https://twitter.com/search?f=tweets&vertical=news&q=%23news&src=unkn"
]
)
}
fn get_url_to_get_random_number() -> String {
"https://www.random.org/integers/?num=1&min=0&max=500&col=1&base=10&format=plain&rnd=new".to_owned()
}
async fn read_number_from_stdin() -> Result<u16, Error> {
use tokio::*;
use futures::stream::StreamExt;
let map_parse_error =
|value|
move |error|
format_err!("Value from stdin isn't a correct `u16`: {:?}, input: {}", error, value);
let mut result;
let mut reader = codec::FramedRead::new(io::BufReader::new(io::stdin()), codec::LinesCodec::new());
while {
println!("Please, enter number (`u16`)");
let next = reader.next();
result = union_async! {
next
|> |value| value.ok_or(format_err!("Unexpected end of input"))
=> |result| ready(result.map_err(|err| format_err!("Failed to apply codec: {:?}", err)))
=> |value|
ready(
value
.parse()
.map_err(map_parse_error(value))
)
!> |error| { eprintln!("Error: {:#?}", error); error}
}.await;
result.is_err()
} {}
result
}
#[tokio::main]
async fn main() {
println!(
"{} {}\n{}",
"Hello.\nThis's is the game where winner is player, which abs(value) is closest to",
"the max count of links (starting with `https://`) found on one of random pages.",
"You play against random generator (0-500)."
);
enum GameResult {
Won,
Lost,
Draw
}
let client = Client::new();
let game = union_async! {
// Make requests to several sites
// and calculate count of links starting from `https://`
get_urls_to_calculate_link_count()
|> {
// If pass block statement instead of fn, it will be placed before current step,
// so it will us allow to capture some variables from context
let ref client = client;
move |url| {
let client = client.clone();
// `union_async!` wraps its content into `async move { }`
union_async! {
client
.get(url).send()
=> |value| value.text()
=> |body| ok((url, body))
}
}
}
>.collect::<Vec<_>>()
|> Ok
=> try_join_all
!> |err| format_err!("Error retrieving pages to calculate links: {:#?}", err)
=> |results|
ok(
results
.into_iter()
.map(|(url, body)| (url, body.matches("https://").collect::<Vec<_>>().len()))
.max_by_key(|(_, link_count)| link_count.clone())
.unwrap()
)
// It waits for input in stdin before log max links count
~?> |result| {
result
.as_ref()
.map(
|(url, count)| {
let split = url.to_owned().split('/').collect::<Vec<_>>();
let domain_name = split.get(2).unwrap_or(&url);
println!("Max `https://` link count found on `{}`: {}", domain_name, count)
}
)
.unwrap_or(());
},
// In parallel it makes request to the site which generates random number
get_url_to_get_random_number()
-> ok
=> {
// If pass block statement instead of fn, it will be placed before current step,
// so it will allow us to capture some variables from context
let client = client.clone();
let map_parse_error =
|value|
move |err|
format_err!("Failed to parse random number: {:#?}, value: {}", err, value);
move |url| {
union_async! {
client
.get(&url)
.send()
=> |value| value.text()
!> |err| format_err!("Error retrieving random number: {:#?}", err)
=> |value| ok(value[..value.len() - 1].to_owned()) // remove \n from `154\n`
=> |value|
ready(
value
.parse::<u16>()
.map_err(map_parse_error(value))
)
}
}
}
// It waits for input in stdin before log random value
~?> |random| {
random
.as_ref()
.map(|number| println!("Random: {:?}", number))
.unwrap_or(());
},
// In parallel it reads value from stdin
read_number_from_stdin(),
// Finally, when we will have all results, we can decide, who is winner
map => |(_url, link_count), random_number, number_from_stdin| {
let random_diff = (link_count as i32 - random_number as i32).abs();
let stdin_diff = (link_count as i32 - number_from_stdin as i32).abs();
match () {
_ if random_diff > stdin_diff => GameResult::Won,
_ if random_diff < stdin_diff => GameResult::Lost,
_ => GameResult::Draw
}
}
};
let _ = game.await.map(
|result|
println!(
"You {}",
match result {
GameResult::Won => "won!",
GameResult::Lost => "lose...",
_ => "have the same result as random generator!"
}
)
).unwrap();
}
```
## Combinators
- Map: `|>` expr - `value`.map(`expr`)
- AndThen: `=>` expr - `value`.and_then(`expr`),
- Then: `->` expr - `expr`(`value`)
- Dot: `>.` expr - `value`.`expr`
- Or: `<|` expr - `value`.or(`expr`)
- OrElse: `<=` expr - `value`.or_else(`expr`)
- MapErr: `!>` expr - `value`.map_err(`expr`)
where `value` is the previous value.
Every combinator prefixed by `~` will act as deferred action (all actions will wait until completion in every step and only after move to the next one).
## Handler
might be one of
- `and_then` => will act as results.and_then(|(result0, result1, ..)| handler(result0, result1, ..))
- `then` => will act as handler(result0, result1, ..)
or not specified - then Result<(result0, result1, ..), Error> or Option<(result0, result1, ..)> will be returned.
## Custom futures crate path
You can specify custom path (`futures_crate_path`) at the beginning of macro call
```rust
use union::union_async;
use futures::future::ok;
#[tokio::main]
async fn main() {
let value = union_async! {
futures_crate_path(::futures)
ok::<_,u8>(2u16)
}.await.unwrap();
println!("{}", value);
}
```
## Single thread combinations
### Simple results combination
Converts input in series of chained results and joins them step by step.
```rust
use std::error::Error;
use union::union;
type Result<T> = std::result::Result<T, Box<dyn Error>>;
fn action_1() -> Result<u16> {
Ok(1)
}
fn action_2() -> Result<u8> {
Ok(2)
}
fn main() {
let sum = union! {
action_1(),
action_2().map(|v| v as u16),
action_2().map(|v| v as u16 + 1).and_then(|v| Ok(v * 4)),
action_1().and_then(|_| Err("5".into())).or(Ok(2)),
map => |a, b, c, d| a + b + c + d
}.expect("Failed to calculate sum");
println!("Calculated: {}", sum);
}
```
### Futures combination
Each branch will represent chain of tasks. All branches will be joined using `join!` macro and macro will return `unpolled` future.
```rust
#![recursion_limit="256"]
use std::error::Error;
use union::union_async;
use futures::future::{ok, err};
type Result<T> = std::result::Result<T, Box<dyn Error>>;
async fn action_1() -> Result<u16> {
Ok(1)
}
async fn action_2() -> Result<u8> {
Ok(2)
}
#[tokio::main]
async fn main() {
let sum = union_async! {
action_1(),
action_2().and_then(|v| ok(v as u16)),
action_2().map(|v| v.map(|v| v as u16 + 1)).and_then(|v| ok(v * 4u16)),
action_1().and_then(|_| err("5".into())).or_else(|_| ok(2u16)),
and_then => |a, b, c, d| ok(a + b + c + d)
}.await.expect("Failed to calculate sum");
println!("Calculated: {}", sum);
}
```
## Multi-thread combinations
To execute several tasks in parallel you could use `union_spawn!` (`spawnion!`) for sync tasks
and `union_async_spawn!` (`async_spawn!`) for futures. Since `union_async` already provides parallel futures execution in one thread, `union_async_spawn!` spawns every branch into `tokio` executor so they will be evaluated in multi-threaded executor.
### Multi-thread sync branches
`union_spawn` spawns one `::std::thread` per each step of each branch (number of branches is the max thread count at the time).
```rust
use std::error::Error;
use union::union_spawn;
type Result<T> = std::result::Result<T, Box<dyn Error + Send + Sync>>;
fn action_1() -> Result<usize> {
Ok(1)
}
fn action_2() -> Result<u16> {
Ok(2)
}
fn main() {
// Branches will be executed in parallel
let sum = union_spawn! {
action_1(),
action_2().map(|v| v as usize),
action_2().map(|v| v as usize + 1).and_then(|v| Ok(v * 4)),
action_1().and_then(|_| Err("5".into())).or(Ok(2)),
map => |a, b, c, d| a + b + c + d
}.expect("Failed to calculate sum");
println!("Calculated: {}", sum);
}
```
`union_async_spawn!` uses `::tokio::spawn` function to spawn tasks so it should be done inside `tokio` runtime
(number of branches is the max count of `tokio` tasks at the time).
### Multi-thread futures
```rust
#![recursion_limit="256"]
use std::error::Error;
use union::union_async_spawn;
use futures::future::{ok, err};
type Result<T> = std::result::Result<T, Box<dyn Error + Send + Sync>>;
async fn action_1() -> Result<u16> {
Ok(1)
}
async fn action_2() -> Result<u8> {
Ok(2)
}
#[tokio::main]
async fn main() {
let sum = union_async_spawn! {
action_1(),
action_2().and_then(|v| ok(v as u16)),
action_2().map(|v| v.map(|v| v as u16 + 1)).and_then(|v| ok(v * 4u16)),
action_1().and_then(|_| err("5".into())).or_else(|_| ok(2u16)),
and_then => |a, b, c, d| ok(a + b + c + d)
}.await.expect("Failed to calculate sum");
println!("Calculated: {}", sum);
}
```
Using combinators we can rewrite first sync example like
```rust
use std::error::Error;
use union::union;
type Result<T> = std::result::Result<T, Box<dyn Error>>;
fn action_1() -> Result<u16> {
Ok(1)
}
fn action_2() -> Result<u8> {
Ok(2)
}
fn main() {
let sum = union! {
action_1(),
action_2() |> |v| v as u16,
action_2() |> |v| v as u16 + 1 => |v| Ok(v * 4),
action_1() => |_| Err("5".into()) <| Ok(2),
map => |a, b, c, d| a + b + c + d
}.expect("Failed to calculate sum");
println!("Calculated: {}", sum);
}
```
By separating chain in actions, you will make actions wait for completion of all of them in current step before go to the next step.
```rust
#![recursion_limit="256"]
use std::error::Error;
use union::union;
type Result<T> = std::result::Result<T, Box<dyn Error + Send + Sync>>;
fn action_1() -> Result<u16> {
Ok(1)
}
fn action_2() -> Result<u8> {
Ok(2)
}
fn main() {
let sum = union! {
action_1(),
let result_1 = action_2() ~|> |v| v as u16 + 1,
action_2() ~|> {
let result_1 = result_1.as_ref().ok().map(Clone::clone);
move |v| {
// `result_1` now is the result of `action_2()` [Ok(1u8)]
if result_1.is_some() {
v as u16 + 1
} else {
unreachable!()
}
}
} ~=> {
let result_1 = result_1.as_ref().ok().map(Clone::clone);
move |v| {
// `result_1` now is the result of `|v| v as u16 + 1` [Ok(2u16)]
if let Some(result_1) = result_1 {
Ok(v * 4 + result_1)
} else {
unreachable!()
}
}
},
action_1() ~=> |_| Err("5".into()) <| Ok(2),
map => |a, b, c, d| a + b + c + d
}.expect("Failed to calculate sum");
println!("Calculated: {}", sum);
}
```