Gem::Dependency#requirement

# File tmp/rubies/ruby-3.1.3/lib/rubygems/dependency.rb, line 117
def requirement
  return @requirement if defined?(@requirement) && @requirement

  # @version_requirements and @version_requirement are legacy ivar
  # names, and supported here because older gems need to keep
  # working and Dependency doesn't implement marshal_dump and
  # marshal_load. In a happier world, this would be an
  # attr_accessor. The horrifying instance_variable_get you see
  # below is also the legacy of some old restructurings.
  #
  # Note also that because of backwards compatibility (loading new
  # gems in an old RubyGems installation), we can't add explicit
  # marshaling to this class until we want to make a big
  # break. Maybe 2.0.
  #
  # Children, define explicit marshal and unmarshal behavior for
  # public classes. Marshal formats are part of your public API.

  # REFACTOR: See above

  if defined?(@version_requirement) && @version_requirement
    version = @version_requirement.instance_variable_get :@version
    @version_requirement = nil
    @version_requirements = Gem::Requirement.new version
  end

  @requirement = @version_requirements if defined?(@version_requirements)
end