[ruby-core:111923] [Ruby master Bug#19286] What should kwargs' arity be?

Issue #19286 has been updated by mame (Yusuke Endoh).


Discussed at the dev meeting. @matz said the current behavior is fair, and @matsuda agreed with that. So keep it as is.

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Bug #19286: What should kwargs' arity be?
https://bugs.ruby-lang.org/issues/19286#change-101346

* Author: matsuda (Akira Matsuda)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.3.0dev (2022-12-28T16:43:05Z master cada537040) +YJIT [arm64-darwin21]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
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Hello, guys. It's time for a quick Ruby quiz.

Q: What is this method's arity?
def f(a:, b:)
end

It requires two arguments, hence it should be 2?
Or if we call this method with one argument, the error message says "wrong number of arguments (given 1, expected 0; required keywords: a, b) (ArgumentError)", which means the arity is 0, maybe?

A: The answer is,
$ all-ruby -e 'p method(def f(a:, b:) end).arity'
ruby-2.1.0-preview1 0
...
ruby-2.1.0          0
ruby-2.1.1          -1
ruby-2.1.2          1
...
ruby-3.1.0          1

it's been 1 since 2.1.2. But why 1? Why not 2 nor 0?

I asked this question to the ruby-core people, and ko1's answer was that even he has no idea what the number 1 means.
![](random_-_ruby-lang_-_Slack.png)

So I thought it'd be worth asking this question here.

---Files--------------------------------
random_-_ruby-lang_-_Slack.png (40.1 KB)


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