ruby-core

Issue #15078 has been updated by akr (Akira Tanaka).


mame (Yusuke Endoh) wrote:
> akr (Akira Tanaka) wrote:
> > How about def `m(**kw) end` binds kw to nil if the last Hash argument is not taken as keyword arguments and
> > `m(**{})` add {} and `m(**nil)` don't add anything to arguments.
> 
> I agree that it is one of the reasonable design choices, but does it break the following code?
> 
> ```
> def foo(**kw)
>   kw[:key]
> end
> 
> foo()
> ```

Yes.  I hope that the incompatibility is acceptable.

If it is not acceptable, I have second idea:
We can use a special frozen empty Hash object instead of nil.

```
NO_KEYWORD_ARGUMENTS = {}.freeze
```

In this idea, the condition of "no keyword argument" is represented as
`NO_KEYWORD_ARGUMENTS.equal?(x)` instead of `nil.equal?(x)`.

It is still incompatible because it is not modifiable, though.

```
def foo(**kw) kw[0] = 1 end; foo()
```

If kw is bind to NO_KEYWORD_ARGUMENTS, `kw[0] = 1` raises FrozenError.

Also, more importantly, it adds a new constant and
we (Ruby programmers) need to remember the name.




----------------------------------------
Bug #15078: Hash splat of empty hash should not create a positional argument.
https://bugs.ruby-lang.org/issues/15078#change-74088

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
* ruby -v: ruby 2.6.0dev (2018-08-27 trunk 64545) [x86_64-darwin15]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
Looks like #10856 is not completely fixed, but I can't reopen it

```
def foo(*args); args; end
foo(**{}) # => []
foo(**Hash.new) # => [{}], should be []
```



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