Localization in Ruby on Rails: Yes/No, on/Off

Ruby on Rails uses the gem psych to load the YAML files for locales.

If you have something like this in your en.yml file:

en: terms: yes: Yes no: No switch_on: On switch_off: Off accept: true reject: false

And then you will try to load them via Rails console like this:

I18n.locale = :en I18n.backend.send(:translations)[:en][:terms]

Notice there that there is no key yes, no and more so all values Yes, No, On Off, true, false were converted to TrueClass or FalseClass in Ruby.

That for me was quite interesting so I dig deeper to understand why this is happening.

Ruby on Rails loads locales using the gem i18n for locales. And that gem is using psych or yaml (which is aliased from psych - see https://github.com/ruby/yaml)

Processing YES, yes, NO, no, on, ON, off, OFF …

Looking at psych here are some tests that we can run:

assert_equal true, Psych.safe_load("--- YES") assert_equal true, Psych.safe_load("--- Yes") assert_equal true, Psych.safe_load("--- yes") assert_equal true, Psych.safe_load("--- TRUE") assert_equal true, Psych.safe_load("--- True") assert_equal true, Psych.safe_load("--- true") assert_equal true, Psych.safe_load("--- ON") assert_equal true, Psych.safe_load("--- on") assert_equal true, Psych.safe_load("--- On")

Notice that it will transform all of those values in TrueClass / true .

If we then run these tests it will return FalseClass / false :

assert_equal false, Psych.safe_load("--- NO") assert_equal false, Psych.safe_load("--- No") assert_equal false, Psych.safe_load("--- no") assert_equal false, Psych.safe_load("--- FALSE") assert_equal false, Psych.safe_load("--- False") assert_equal false, Psych.safe_load("--- false") assert_equal false, Psych.safe_load("--- OFF") assert_equal false, Psych.safe_load("--- Off") assert_equal false, Psych.safe_load("--- off")

Could not find the exact documentation about this but it seems like psych implements YAML version 1.1 that defines the following:

Notice there that it also defines Y, y, N, n as booleans.

assert_equal "Y", Psych.safe_load("--- Y") assert_equal "y", Psych.safe_load("--- y") assert_equal "N", Psych.safe_load("--- N") assert_equal "n", Psych.safe_load("--- n")

But in our case when psych does not do that.

Why Psych does not convert Y, y, N, n to booleans?

The difference is documented for example in psych gem test suite for example:

def test_y assert_equal "y", Psych.load("--- y") assert_equal "Y", Psych.load("--- Y") end def test_n assert_equal "n", Psych.load("--- n") assert_equal "N", Psych.load("--- N") end

syck was an old parser for YAML written in C that seems to have been implemented since Ruby 1.9 (maybe even earlier) and syck implemented YAML version 1.0. See https://ruby-doc.org/stdlib-1.9.3/libdoc/syck/rdoc/Syck.html

I could not find the exact specification in YAML version 1.0 that defines the booleans so it could be there was a discussion about this and syck, as the YAML parser implemented in C and used by Ruby, decided to adopt it.

Here is the test_boolean.rb from syck and notice there YAML spec says "y" and "Y" may be used as true, but Syck treats them # as literal strings

def test_y assert_equal "y", Psych.load("--- y") assert_equal "Y", Psych.load("--- Y") end def test_n assert_equal "n", Psych.load("--- n") assert_equal "N", Psych.load("--- N") end