Bug #11860: Double splat does not work on empty hash assigned via variable

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 2.3.0preview2 (2015-12-11 trunk 53028) [x86_64-linux]
• Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN

[sawa (Tsuyoshi Sawada)]

When an empty hash is given as a literal, the double splat operates on it, and leaves nothing, which is expected.

class String
  def foo; end
end

[**{}] # => []
"foo".foo(**{}) # => nil
"foo".send("foo", **{}) # => nil

However, when an empty hash is given via variable, the double splat retains an empty hash in place.

h = {}

[**h] # => [{}]
"foo".foo(**h) # => wrong number of arguments (given 1, expected 0)
"foo".send("foo", **h) # => wrong number of arguments (given 1, expected 0)

[sawa (Tsuyoshi Sawada)]

I found more cases (other than via variable) that the double splat does not work on an empty hash. While parenthesis or nesting does not cause the issue:

[**({})] # => []
[**begin {} end] # => []
[**{**{}}] # => []

more complicated expressions seem to cause the issue:

[**({} if true)] # => [{}]
[**(if true; {} end)] # => [{}]
[**(false ? :foo : {})] # => [{}]

[justcolin (Colin Fulton)]

A similar bug happens when using the double splat operator in the parameter list of a method definition. See #12022.

[sawa (Tsuyoshi Sawada)]

This bug is related to #10708.

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

[sawa (Tsuyoshi Sawada)]

• Description updated (diff)

[jeremyevans0 (Jeremy Evans)]

• Related to Feature #14183: "Real" keyword argument added

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed

With recent commits to the master branch, keyword splats of empty hashes do not pass positional arguments to methods or cause an empty hash to be added to an array.