[ruby-core:89038] [Ruby trunk Bug#15078] Hash splat of empty hash should not create a positional argument.

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


mame (Yusuke Endoh) wrote:

> ```
> def target(*args)
>   p args
> end
> 
> def forward(*args, **kw, &blk)
>   target(*args, **kw, &blk)
> end
> 
> target(1, 2, 3, {})  #=> [1, 2, 3, {}]
> forward(1, 2, 3, {}) #=> [1, 2, 3] on the semantics you proposed ([1, 2, 3, {}] on the current behavior)
> ```
> 
> Akr-san said that it would be impossible to create a "perfect" semantics to satisfy all cases.  In Ruby 2.X, he said that `**empty_hash` should be just ignored, and that `foo({}, **{})` should be always equal to `foo({})`, even if `def foo(opt=42, **kw)` receives `opt=42`.  (However, matz showed reluctance to this behavior.  So, the solution for this ticket is not decided yet.)

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.

{}/nil distinguish there are keyword arguments or not.
This information is what lacks to implement perfect delegation method.

In this behavior, following two should be same behavior (in Ruby 2.X), I think.

```
def f(*a, *kw) g(*a, *kw) end
def f(*a) g(*a) end
```

----------------------------------------
Bug #15078: Hash splat of empty hash should not create a positional argument.
https://bugs.ruby-lang.org/issues/15078#change-74065

* 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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