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


Sorry, it seems my original description was unclear.  I think it can be rephased very simply:

* keyword argument MUST be always received as a keyword parameter
* non-keyword argument MUST be always received as a non-keyword parameter

The following behavior will be abandoned:

* keyword argument is passed to a last normal parameter
* last normal hash argument is passed to keyword parameters

[Here is an experimental patch](https://gist.github.com/mame/60c7eb4060506158c95141054bde6d86) to warn a deprecated behavior of keyword arguments, and it shows some OK/NG samples.

## NG: a keyword argument is passed to a normal parameter

```
$ ./miniruby -w -e '
def foo(h)
end
foo(k: 1)
'
-e:4: warning: The keyword argument for `foo' is used as the last parameter
```

## OK: receving it as a keyword rest argument

```
$ ./miniruby -w -e '
def foo(**h)
end
foo(k: 1)
'
```

## NG: a normal hash argument is passed to a keyword argument

```
$ ./miniruby -w -e '
def foo(k: 1)
end
h = {k: 42}
foo(h)
'
-e:5: warning: The last argument for `foo' is used as the keyword parameter
```

## OK: the hash as keyword argument by using `**`

```
$ ./miniruby -w -e '
def foo(k: 1)
end
h = {k: 42}
foo(**h)
'
```

It still needs more work.  It does not support yet methods written in C because C methods always handles keyword arguments as normal arguments.

----------------------------------------
Feature #14183: "Real" keyword argument
https://bugs.ruby-lang.org/issues/14183#change-73075

* 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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