Issue #10708 has been updated by David Unric.


By my subjective opinion I don't find this a bug but a feature.

> Consider this:
> def foo; end
> foo(*[]) #Splatting an empty list is ok
> foo(**{}) #Double splatting an empty hash is like calling foo({}) which gives an error

Here you define a method without a (keyword) argument placeholder so it does not expect a Hash argument, which is effectively used to pass keyword arguments at method call, even when keyword arguments are empty. Note calling `foo(kwarg: 'value')` is just a syntactic sugar to `foo({kwarg: 'value'})`.
Methods unlike procs do check arguments count, so ArgumentError exception is the correct behavior.

This is an expected difference to expanding an Array, which results in *plain arguments list* which can result in *"nothing"*, ie. an empty list. `foo(*[])` is interpreted as `foo()` so you won't get an error.

You probably assume expanding a Hash, ie. applying double-splat operator on empty Hash instance at method call would behave the same way. However implementing such a special corner-case behavior would only introduce inconsistency in the language or would require implementing a *quite new different type of plain list* like *"plain keyword arguments list"*.


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Bug #10708: In a function call, double splat of an empty hash still calls the function with an argument
https://bugs.ruby-lang.org/issues/10708#change-50867

* Author: Damien Robert
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: ruby 2.2.0p0 (2014-12-25 revision 49005) [x86_64-linux]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
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Consider this:
    def foo; end
    foo(*[]) #Splatting an empty list is ok
    foo(**{}) #Double splatting an empty hash is like calling foo({}) which gives an error

This is annoying in a function that is a wrapper around another function and just process some keywords:
    def wrapper(*args, keyword: true, **others)
      puts keyword
      wrappee(*args,**others) #here this code will fail if others is empty
    end



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