nushell/crates/nu-command
Devyn Cairns 872aa78373
Add interleave command for reading multiple streams in parallel (#11955)
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# Description
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This command mixes input from multiple sources and sends items to the
final stream as soon as they're available. It can be called as part of a
pipeline with input, or it can take multiple closures and mix them that
way.

See `crates/nu-command/tests/commands/interleave.rs` for a practical
example. I imagine this will be most often used to run multiple commands
in parallel and print their outputs line-by-line. A stdlib command could
potentially use `interleave` to make this particular use case easier.

It's quite common to wish that nushell had a command for running things
in the background, and instead of providing job control, this provides
an alternative to some use cases for that by just allowing multiple
commands to run simultaneously and direct their output to the same
place.

This enables certain things that are not possible with `par-each` - for
example, you may wish to run `make` across several projects in parallel:

```nushell
(ls projects).name | par-each { |project| cd $project; make }
```

This works well enough, but the output will only be available after each
`make` command finishes. `interleave` allows you to get each line:

```nushell
interleave ...(
  (ls projects).name | each { |project|
    {
      cd $project
      make | lines | each { |line| {project: $project, out: $line} }
    }
  }
)
```

The result of this is a stream that you could process further - for
example, by saving to a text file.

Note that the closures themselves are not run in parallel. The initial
execution happens serially, and then the streams are consumed in
parallel.

# User-Facing Changes
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Adds a new command.

# Tests + Formatting
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- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting
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2024-03-01 16:56:37 -06:00
..
src Add interleave command for reading multiple streams in parallel (#11955) 2024-03-01 16:56:37 -06:00
tests Add interleave command for reading multiple streams in parallel (#11955) 2024-03-01 16:56:37 -06:00
Cargo.toml Bump mockito from 1.2.0 to 1.3.0 (#11976) 2024-02-26 15:38:29 +08:00
LICENSE Fix rest of license year ranges (#8727) 2023-04-04 09:03:29 +12:00