module RSpec::Core::MemoizedHelpers

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.included(mod)
  mod.extend(ClassMethods)
  # This logic defines an implicit subject
  mod.subject do
    described = described_class || self.class.description
    Class === described ? described.new : described
  end
end

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

def __memoized
  @__memoized ||= {}
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
  raise NotImplementedError, 'This definition is here for documentation purposes only'
    ' - it is overriden anyway below when this module gets included.'
end