Issue #14183 has been updated by mame (Yusuke Endoh).


Jeremy, thank you for investigating the examples.  I'd like to discuss this issue at the next developers' meeting.

This is my personal current opinion: this change indeed requires users' action, however, I believe that the problem is not so significant, and that its advantage is significant.

This change seems to remind you the breaking change of character encoding in 1.9/2.0, but it was much worse than this change because the previous one was not trivial "where to fix".  The site where an error occurred was often different to the site where a wrong encoding string was created.
On the other hand, this change requires very trivial fixes.  By running a test suite on Ruby 2.6 or 2.7, the interpreter will "pinpoint" all usages like you showed, and warn "this method call in line XX will not work in Ruby 3.x!".  Users can easily fix the issue by checking the warnings and changing either the method calls or method definition.

I agree that compatibility is important, but the current wrong design has continuously caused troubles.  This fact also looks important to me.  This change will fix the issue, will make the language simpler, and will make users' code more explicit and less error-prone, which will pay users' action.

----------------------------------------
Feature #14183: "Real" keyword argument
https://bugs.ruby-lang.org/issues/14183#change-73814

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: Next Major
----------------------------------------
In RubyWorld Conference 2017 and RubyConf 2017, Matz officially said that Ruby 3.0 will have "real" keyword arguments.  AFAIK there is no ticket about it, so I'm creating this (based on my understanding).

In Ruby 2, the keyword argument is a normal argument that is a Hash object (whose keys are all symbols) and is passed as the last argument.  This design is chosen because of compatibility, but it is fairly complex, and has been a source of many corner cases where the behavior is not intuitive.  (Some related tickets: #8040, #8316, #9898, #10856, #11236, #11967, #12104, #12717, #12821, #13336, #13647, #14130)

In Ruby 3, a keyword argument will be completely separated from normal arguments.  (Like a block parameter that is also completely separated from normal arguments.)
This change will break compatibility; if you want to pass or accept keyword argument, you always need to use bare `sym: val` or double-splat `**` syntax:

```
# The following calls pass keyword arguments
foo(..., key: val)
foo(..., **hsh)
foo(..., key: val, **hsh)

# The following calls pass **normal** arguments
foo(..., {key: val})
foo(..., hsh)
foo(..., {key: val, **hsh})

# The following method definitions accept keyword argument
def foo(..., key: val)
end
def foo(..., **hsh)
end

# The following method definitions accept **normal** argument
def foo(..., hsh)
end
```

In other words, the following programs WILL NOT work:

```
# This will cause an ArgumentError because the method foo does not accept keyword argument
def foo(a, b, c, hsh)
  p hsh[:key]
end
foo(1, 2, 3, key: 42)

# The following will work; you need to use keyword rest operator explicitly
def foo(a, b, c, **hsh)
  p hsh[:key]
end
foo(1, 2, 3, key: 42)

# This will cause an ArgumentError because the method call does not pass keyword argument
def foo(a, b, c, key: 1)
end
h = {key: 42}
foo(1, 2, 3, h)

# The following will work; you need to use keyword rest operator explicitly
def foo(a, b, c, key: 1)
end
h = {key: 42}
foo(1, 2, 3, **h)
```

I think here is a transition path:

* Ruby 2.6 (or 2.7?) will output a warning when a normal argument is interpreted as keyword argument, or vice versa.
* Ruby 3.0 will use the new semantics.



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