module RSpec::Core::MemoizedHelpers

def self.module_for(example_group)
  get_constant_or_yield(example_group, :LetDefinitions) do
    # Expose `define_method` as a public method, so we can
    # easily use it below.
    mod = Module.new { public_class_method :define_method }
    example_group.__send__(:include, mod)
    example_group.const_set(:LetDefinitions, mod)
    mod
  end
end