Issue #17197 has been updated by mame (Yusuke Endoh).


Ah, I was wrong.

mame (Yusuke Endoh) wrote in #note-6:
> IMO, this is a bug since 1.9.0 because Hash#select looks like a faster version of Enumerable#select, so it should behave as possible as like Enumerable#select.

Hash#select returns a hash instead of an array, so Hash#select is not a simple faster variant of Enumerable#select. So it don't necessarily have to follow the arity.


Just for the record: I found one affected use case of `Hash#select` with one-arity block in [a popular gem](https://rubygems.org/gems/docker-api):

https://github.com/swipely/docker-api/blob/1e9b9cc5f0f38dcd54c18189812328bb802d3656/lib/docker/container.rb#L327

```
  def self.create(opts = {}, conn = Docker.connection)
    query = opts.select {|key| ['name', :name].include?(key) }
```

It is very difficult to find this kind of cases by gem-codesearch, so I guess there are more cases.

----------------------------------------
Bug #17197: Some Hash methods still have arity 2 instead of 1
https://bugs.ruby-lang.org/issues/17197#change-88552

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* Assignee: nobu (Nobuyoshi Nakada)
* ruby -v: ruby 3.0.0dev (2020-09-26T17:38:39Z master 950614b088)
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
`Hash#each` was changed recently to have arity of 1.
All other methods of `Hash` should behave the same.
Much has been fixed since #14015, but some remains:

```ruby
# Some methods consistently have arity 2:
{a: 1}.select( &->(_kvp) {} ) # => ArgumentError (wrong number of arguments (given 2, expected 1))
```

All in all: `%i[select keep_if delete_if reject to_h]` have their arity still set at 2.




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