Issue #14183 has been updated by bughit (bug hit).


> That was already legal if foo did not accept keyword arguments. :)

my full example was this

```rb
def foo(a: nil, **args)
  args
end

foo(a: 1, 'a' => 2, 1 => 3, nil => 4, true => 5, Object.new => 6)

```

This is not legal in 2.6 and will be in 2.7, somehow in the name of "real keyword arguments"

> One person's "useful destructuring" is another person's "bad hack".

destructuring itself can not be called a hack, it's a feature of many languages ruby competes with and will likely make it back to ruby.

>  Keyword arguments were not intended for destructuring

It is irrelevant what the intent was, it was present and was useful and is therefore an unwelcome breaking change, unless first-class destructuring is added.

> Ignoring backwards compatibility, do you think the previous way of handling keyword arguments was better?

I did not even suggest reverting it. I said make it even more "real" by blocking `foo(a: 1, 'a' => 2, 1 => 3, nil => 4, true => 5, Object.new => 6)` and provide first-class hash param destructuring when taking away the current one, in 3.0.






----------------------------------------
Feature #14183: "Real" keyword argument
https://bugs.ruby-lang.org/issues/14183#change-83114

* Author: mame (Yusuke Endoh)
* Status: Closed
* 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.

---Files--------------------------------
vm_args.diff (4.19 KB)
vm_args_v2.diff (4.18 KB)


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