module RSpec::Core::MemoizedHelpers

def self.module_for(example_group)
  get_constant_or_yield(example_group, :LetDefinitions) do
    mod = Module.new do
      include Module.new {
        example_group.const_set(:NamedSubjectPreventSuper, self)
      }
    end
    example_group.const_set(:LetDefinitions, mod)
    mod
  end
end