示例

有限数字流

use async_fn_stream::fn_stream;
use futures_util::Stream;

fn build_stream() -> impl Stream<Item = i32> {
    fn_stream(|emitter| async move {
        for i in 0..3 {
            // yield elements from stream via `emitter`
            emitter.emit(i).await;
        }
    })
}

从文本文件读取数字，带有错误处理

use anyhow::Context;
use async_fn_stream::try_fn_stream;
use futures_util::{pin_mut, Stream, StreamExt};
use tokio::{
    fs::File,
    io::{AsyncBufReadExt, BufReader},
};

fn read_numbers(file_name: String) -> impl Stream<Item = Result<i32, anyhow::Error>> {
    try_fn_stream(|emitter| async move {
        // Return errors via `?` operator.
        let file = BufReader::new(File::open(file_name).await.context("Failed to open file")?);
        pin_mut!(file);
        let mut line = String::new();
        loop {
            line.clear();
            let byte_count = file
                .read_line(&mut line)
                .await
                .context("Failed to read line")?;
            if byte_count == 0 {
                break;
            }

            for token in line.split_ascii_whitespace() {
                let Ok(number) = token.parse::<i32>() else {
                    // Return errors via the `emit_err` method.
                    emitter.emit_err(
                        anyhow::anyhow!("Failed to convert string \"{token}\" to number")
                    ).await;
                    continue;
                };
                emitter.emit(number).await;
            }
        }

        Ok(())
    })
}

为什么不使用async-stream？

async-stream 很棒！它有很好的语法，但它基于宏，这带来了一些缺陷。

• proc宏有时与Rust-analyzer或IntelliJ Rust等IDE交互不好。例如，https://github.com/rust-lang/rust-analyzer/issues/11533
• proc-macros可能会增加构建时间