[ruby-core:96010] [Ruby master Feature#16261] Enumerable#each_splat and Enumerator#splat

Issue #16261 has been updated by knu (Akinori MUSHA).


I agree this feature would be a nice addition.

Actually I had exactly the same idea, presented at Rails Developer Meetup 2019: https://www.slideshare.net/akinorimushaevolution-of-enumerator

There's a subtle difference between Hash#each/map and Hash#select/reject in how they yield each key-value pair.

```ruby
{a:1,b:2}.select{|x|p x}
# :a
# :b
{a:1,b:2}.each{|x|p x}
# [:a, 1]
# [:b, 2]
```

I guess this was an unintended difference, but we cannot fix it by now for compatibility reasons, and each_splat would be one way to work around it.

----------------------------------------
Feature #16261: Enumerable#each_splat and Enumerator#splat
https://bugs.ruby-lang.org/issues/16261#change-82848

* Author: zverok (Victor Shepelev)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
**UPD:** After discussion in comments, method names changed to "splat"-based.

New methods proposal.

Prototype code:
```ruby
module Enumerable
  def each_splat
    return to_enum(__method__) unless block_given?
    each_entry { |item| yield(*item) } # unpacking possible array into several args
  end
end

class Enumerator
  def splat
    return to_enum(:splat) unless block_given?
    each_entry { |item| yield(*item) }
  end
end
```

Supposed documentation/explanation:

> For enumerable with Array items, passes all items in the block provided as a separate arguments. t could be useful if the provided block has lambda semantics, e.g. doesn't unpack arguments automatically. For example:

  ```ruby
files = ["README.md", "LICENSE.txt", "Contributing.md"]
content = [fetch_readme, fetch_license, fetch_contributing] # somehow make a content for the files

files.zip(content).each_splat(&File.:write) # writes to each file its content
```

> When no block passed, returns enumerator of the tuples:

  ```ruby
[1, 2, 3].zip([4, 5, 6]).each_splat.map(&:+) # => [5, 7, 9] 
```



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