Try to catch a uninitialized constant error and then load the missing file and necessary class

const_missing_test.rb

def Object.const_missing(const_name, *args)
  puts "const_missing #{const_name.inspect}"
  require './test_class'
  Object.const_get const_name
end

obj = TestClass.new
puts obj.f # => hello world

test_class.rb

class TestClass
  def f
    'hello world'
  end
end