module RSpec::Core::MemoizedHelpers

def self.define_helpers_on(example_group)
  example_group.__send__(:include, module_for(example_group))
end

def self.get_constant_or_yield(example_group, name)
  if example_group.const_defined?(name)
    example_group.const_get(name)
  else
    yield
  end
end

def self.get_constant_or_yield(example_group, name)
  if example_group.const_defined?(name, (check_ancestors = false))
    example_group.const_get(name, check_ancestors)
  else
    yield
  end
end

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

def __memoized
  @__memoized ||= {}
end

def is_expected
  expect(subject)
end

def should(matcher=nil, message=nil)
  RSpec::Expectations::PositiveExpectationHandler.handle_matcher(subject, matcher, message)
end

def should_not(matcher=nil, message=nil)
  RSpec::Expectations::NegativeExpectationHandler.handle_matcher(subject, matcher, message)
end

def subject
  __memoized.fetch(:subject) do
    __memoized[:subject] = begin
      described = described_class || self.class.description
      Class === described ? described.new : described
    end
  end
end