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


Jeremy, thank you for discussing this issue seriously.

jeremyevans0 (Jeremy Evans) wrote:
> If that was the only change, it wouldn't be a big deal. However, in addition to `foo(:key => val)` calls, there are also `foo(hsh)` calls.  So all callers that pass hashes would need to change from `foo(hsh)` to `foo(**hsh)`.  And that also breaks if there are any non-symbol keys in the hash.

Yes, in the current proposal, you need to rewrite all callers that passes a hash object.  Note that you can already write `foo(**hsh)` in caller side since 2.0 (when callee-side keyword argument was introduced).  Also, I believe it is a good style because the explicit operator clarifies the intent.

I have no strong opinion whether `foo(:kw => 1)` should pass a normal hash argument or be interpreted as keyword argument.  I think the latter is better in terms of compatibility, but I'm not sure.


> If keyword arguments are not part of the method definition, then what is the issue with converting keyword arguments to a hash argument?

I have never thought of this.  I want to reject the following program, 

```
def foo(*ary)
end
foo(kw: 1)
```

but it might be a good idea as a measure for compatibility.


> > It still needs more work.  It does not support yet methods written in C because C methods always handles keyword arguments as normal arguments.
> 
> What will happen to external C extension gems that use `rb_get_kwargs` and `rb_extract_keywords`, both of which accept a hash?

Yes, we need to prepare C API.  Ko1 has had a big plan about this since last year (or older).

----------------------------------------
Feature #14183: "Real" keyword argument
https://bugs.ruby-lang.org/issues/14183#change-73080

* 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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