Bug #16371: Inconsistent usage of Double splat operator

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 2.6.0
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
• Tags: backport

[dmytro.vasin (Dmytro Vasin)]

Here is an issue with a weird behavior of ruby double splat operator:

a = {a: 'a'}
b = {'b' => 'b'}

{x: 'x', **a}
#=> {:x=>"x", :a=>"a"}

{x: 'x', **b}
#=> TypeError (hash key "b" is not a Symbol)

When I do that implicitly, it works:

{x: 'x', **{'b' => 'b'}} 
#=> {:x=>"x", "b"=>"b"}

At the same time:

{**{'b' => 'b'}}
# TypeError (hash key "b" is not a Symbol)

From my point of view, it definitely works inconsistently.

Could you help with this example or give an advice? (maybe I used it incorrectly?)

[mame (Yusuke Endoh)]

** operator is for keyword arguments, and in Ruby 2.6, non-symbol key is not allowed in keyword arguments. So in principle, {x: 'x', **{'b' => 'b'}} should raise an exception.

Because of the spec change of keyword arguments (#14183), non-symbol key is allowed in Ruby 2.7, and all shown cases work without exception.

Do you want the case to raise an exception in Ruby 2.6?

[sawa (Tsuyoshi Sawada)]

• Description updated (diff)

[matz (Yukihiro Matsumoto)]

I think this inconsistency is a bug. Double splat in hash expressions needs to work as interpolation.

Matz.

[mame (Yusuke Endoh)]

matz, the following is the current behaviors. Do you mean which should be fixed?

(1) 2.7, via variable

b = {"b" => "b"}; p({x: "x", **b}) #=> current behavior: {:x=>"x", "b"=>"b"}

(2) 2.6, via variable

b = {"b" => "b"}; p({x: "x", **b}) #=> current behavior: hash key "b" is not a Symbol (TypeError)

(3) 2.7, with literal

p({x: "x", **{"b" => "b"}}) #=> current behavior: {:x=>"x", "b"=>"b"}

(4) 2.6, with literal

p({x: "x", **{"b" => "b"}}) #=> current behavior: {:x=>"x", "b"=>"b"}

[hsbt (Hiroshi SHIBATA)]

• Tags set to backport

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed

Ruby 2.6 is now in security maintenance mode, so behavior of the double splat operator will not be changed in it.