[#67346] Future of test suites for Ruby — Charles Oliver Nutter <headius@...>

I'll try to be brief so we can discuss all this. tl;dr: RubySpec is

19 messages 2015/01/05

[ruby-core:67440] [ruby-trunk - Bug #10708] In a function call, double splat of an empty hash still calls the function with an argument

From: dunric29a@...
Date: 2015-01-09 00:57:10 UTC
List: ruby-core #67440
Issue #10708 has been updated by David Unric.


If I am not mistaken, even latest Ruby 2.2 selects keyword arguments as the=
 last method's argument and of Hash type.

Let's imagine an example where both simple and keyword optional arguments a=
re used:

~~~
def call_multiargs(method, *aopts, **kwopts); send(method, *aopts, **kwopts=
); end
# kwopts can be passed to send method without double-splat operator as it d=
oes _nothing_ here

def args_and_kwargs(*args, **kwargs); p args; p kwargs; end

call_multiargs(:args_and_kwargs, **{a: 1, b:2})
# How should Ruby expand the hash ?
#   - as (:a, 1, :b, 2) list so kwopts would be empty {} ?
#   - as (:a, 1) and {b: 2} so kwopts would be {b: 2} ?
#   - as {a: 1, b:2} so aopts would be empty [] ?
#   - as ([:a, 1], [:b, 2]) list and kwopts would be empty {} ?
#   - as ([:a, 1]) and {:b, 2} ?
#   etc
~~~

Because Ruby has no special keyword list type like Python has and for keywo=
rd arguments a single Hash instance is used, it is fundamentally not possib=
le to do an expansion of `**{=E2=80=A6}` into a list.
Again, in Ruby there does not exist a list of type `:a =3D> 1, :b =3D> 2`. =
What you see in a method call is a syntactic sugar for `{:a =3D> 1, :b =3D>=
 2}`, ie. optional braces.
To keep consistency there can't exist an exception to this rule for empty h=
ashes.

To sum it up, use of double-splat operator for hash expansion is wrong and =
makes no sense.

p.s. As far as I know, there are only two cases and only as a parser syntax=
 helpers for Hash and Array constructors, quite unrelated to some list expa=
nsion:
`{**{:a =3D> 1, :b =3D> 2}}` - enclosed hash items used for implicit form
`[*{:a =3D> 1, :b =3D> 2}]`  - enclosed hash converted with Hash#to_a and u=
sed for implicit form


----------------------------------------
Bug #10708: In a function call, double splat of an empty hash still calls t=
he function with an argument
https://bugs.ruby-lang.org/issues/10708#change-50869

* Author: Damien Robert
* Status: Open
* Priority: Normal
* Assignee:=20
* Category:=20
* Target version:=20
* 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
----------------------------------------
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 an=
d 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



--=20
https://bugs.ruby-lang.org/

In This Thread

Prev Next