Question

Koan code, number 75:

      in_ruby_version("mri") do
        RubyConstant = "What is the sound of one hand clapping?"
        def test_constants_become_symbols
          all_symbols = Symbol.all_symbols

          assert_equal __, all_symbols.include?(__)
        end
      end

I’m a bit confused with it because I’ve just found that any symbol tested against the “all_symbols.include?(__)” will match “true”. For example, all of the following should work:

    assert_equal true, all_symbols.include?(:RubyConstant)
    assert_equal true, all_symbols.include?(:"What is the sound of one hand clapping?")
    assert_equal true, all_symbols.include?(:AnythingElseYouCouldWriteHere)

What is it to learn with “constants_become_symbols” at all?

Answer 1

In ruby, variables that start with capital letters become constants. The goal of the koan is to teach you that constants become symbols in ruby and get added to the ruby’s symbols table.

in_ruby_version("mri") do
  RubyConstant = "What is the sound of one hand clapping?"
  def test_constants_become_symbols
    all_symbols = Symbol.all_symbols

    assert_equal true, all_symbols.include?("RubyConstant".to_sym)
  end
end

Also notice how it says "RubyConstant".to_sym instead of :RubyConstant. It’s to avoid confusion since the ruby interpreter will automatically create a symbol when it parses a ruby function, as explained here.