Inconsistencies with MRI: FrozenError (can't modify frozen array)

[splattael]

Environment

• jruby -v: jruby 9.2.0.0-SNAPSHOT (2.5.0) 2018-05-09 89183d0 OpenJDK 64-Bit Server VM 25.162-b12 on 1.8.0_162-8u162-b12-1~deb9u1-b12 [linux-x86_64]
• Operating system and platform uname -a: Linux toshi 4.9.0-0.bpo.2-amd64 #1 SMP Debian 4.9.18-1~bpo8+1 (2017-04-10) x86_64 GNU/Linux

Given code

a = [].freeze
a << 1

Expected Behavior

In MRI it's

FrozenError (can't modify frozen Array)

Actual Behavior

FrozenError (can't modify frozen array)

Note the lowercase array.

Possible references to other issues

• Inconsistencies with MRI regarding hashes and arrays affecting rails #411

[enebo]

@splattael did this happen to cause something to fail? We are happy to correct this (and this fix fixed a second issue), but did something fail due to the wrong string 'array'?

[splattael]

@enebo Yay, thanks for fixing! 💜

Yes, it caused a test failure which matched the exact error message when using Dry::Struct::Value.

It was something along these lines:

require "dry/struct"
require "dry/types"
require "minitest/autorun"

class Image < Dry::Struct::Value
  attribute :sizes, Array
end

class ImageTest < MiniTest::Test
  def test_immutable
    image = Image.new(sizes: %w[100x100])

    e = assert_raises do
      image.sizes << "200x200"
    end

    assert_equal "can't modify frozen Array", e.message
  end
end

On JRuby it failed with:

Run options: --seed 61393

# Running:

F

Finished in 0.022419s, 44.6049 runs/s, 89.2098 assertions/s.

  1) Failure:
ImageTest#test_immutable [foo2.rb:17]:
Expected: "can't modify frozen Array"
  Actual: "can't modify frozen array"

1 runs, 2 assertions, 1 failures, 0 errors, 0 skips

As a workaround we do:

...
    assert_equal "can't modify frozen array", e.message.downcase
...

Again, thanks for your blazing fast fix 🤓