union!、union_async!、asyncion!、union_spawn!、union_async_spawn!、async_spawn! 宏的导出，由 union 包导出。

union!

union! - 一个统治它们的宏。提供有用的快捷组合子，组合同步/异步链，将结果的元组转换为元组的结果，支持单线程和多线程（同步/异步）逐步执行分支。

使用此宏可以编写如下内容

#![recursion_limit = "256"]

use rand::prelude::*;
use std::sync::Arc;
use union::union_spawn;

fn generate_random_vec<T>(size: usize, max: T) -> Vec<T>
where
    T: From<u8>
        + rand::distributions::uniform::SampleUniform
        + rand::distributions::uniform::SampleBorrow<T>
        + Copy,
{
    let mut rng = rand::thread_rng();
    (0..size)
        .map(|_| rng.gen_range(T::from(0u8), max))
        .collect()
}

fn is_even<T>(value: T) -> bool
where
    T: std::ops::Rem<Output = T> + std::cmp::PartialEq + From<u8>,
{
    value % 2u8.into() == 0u8.into()
}

fn get_sqrt<T>(value: T) -> T
where
    T: Into<f64>,
    f64: Into<T>,
{
    let value_f64: f64 = value.into();
    value_f64.sqrt().into()
}

fn power2<T>(value: T) -> T
where
    T: std::ops::Mul<Output = T> + Copy,
{
    value * value
}

// Problem: generate vecs filled by random numbers in parallel, make some operations on them in parallel,
// find max of each vec in parallel and find final max of 3 vecs

// Solution:
fn main() {
    // Branches will be executed in parallel, each in its own thread
    let max = union_spawn! {
        let branch_0 =
            generate_random_vec(1000, 10000000u64)
                .into_iter()
                // Multiply every element by himself
                |> power2
                >.filter(|value| is_even(*value)).collect::<Vec<_>>()
                // Use `Arc` to share data with branch 1
                -> Arc::new
                ~-> |v: Arc<Vec<_>>| {
                    // Extract raw poiner after sharing
                    let pointer = Arc::into_raw(v);
                    unsafe {(
                        // Find max and clone its value
                        (&*pointer)
                            .iter()
                            .max()
                            .map(Clone::clone),
                        // After this we call `from_raw` to prevent memory leak
                        Arc::from_raw(pointer)
                    )}.0
                },
        generate_random_vec(10000, 100000000000000f64)
            .into_iter()
            // Extract sqrt from every element
            |> get_sqrt
            // Add index in order to compare with the values of branch 0
            >.enumerate()
            ~|> {
                // Get data from branch 0 by cloning arc
                let branch_0 = branch_0.clone();
                let len = branch_0.len();
                // Compare every element of branch 1 with element of branch 0
                // with the same index and take min
                move |(index, value)|
                    if index < len && value as u64 > branch_0[index] {
                        branch_0[index]
                    } else {
                        value as u64
                    }
            }
            >.max(),
        generate_random_vec(100000, 100000u32)
            .into_iter()
            ~>.max(),
        map => |max0, max1, max2|
            // Find final max
            *[max0, max1, max2 as u64].into_iter().max().unwrap()
    }
    .unwrap();
    println!("Max: {}", max);
}

和这样

#![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() -> &'static str {
    "https://www.random.org/integers/?num=1&min=0&max=500&col=1&base=10&format=plain&rnd=new"
}

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|
                    // `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 ref client = client;
                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();  
}

组合子

• 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)

• 检查：?> expr - (|value| { expr(&value); value })(value) 用于同步链，以及 (|value| value.inspect(expr))(value) 用于未来

其中 value 是前一个值。

每个以 ~ 开头的组合器都将作为延迟操作（所有操作将在每个步骤中等待完成，然后才进行下一步）。

处理器

可能是以下之一

• map => 将作为 results.map(|(result0, result1, ..)| handler(result0, result1, ..))

• and_then => 将作为 results.and_then(|(result0, result1, ..)| handler(result0, result1, ..))

• then => 将作为 handler(result0, result1, ..)

或者未指定 - 则返回 Result<(result0, result1, ..), Error> 或 Option<(result0, result1, ..)>。

自定义未来crate路径

您可以在宏调用开始处指定自定义路径（futures_crate_path）。

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);
}

单线程组合

简单结果组合

将输入转换为一系列链式结果，并逐步将它们连接起来。

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);
}

未来组合

每个分支将代表任务链。所有分支都将使用 ::futures::join! 宏和 union_async! 返回 unpolled 未来。

#![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);
}

多线程组合

要并行执行多个任务，可以使用 union_spawn! （spawn!） 用于同步任务和 union_async_spawn! （async_spawn!） 用于未来。由于 union_async 已在单个线程中提供并行未来执行，因此 union_async_spawn! 将每个分支spawn到 tokio 执行器中，因此它们将在多线程执行器中进行评估。

多线程同步分支

union_spawn 为每个分支的每个步骤spawn一个 ::std::thread（分支数是当时最大线程数）。

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! 使用 ::tokio::spawn 函数来spawn任务，因此应该在 tokio 运行时内部进行（分支数是当时 tokio 任务的最大计数）。

多线程未来

#![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);
}

使用组合器，我们可以像下面一样重写第一个同步示例

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);
}

通过在操作中分离链，您将使操作在进入下一步之前等待当前步骤中所有操作的完成。

#![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);
}