A new use for Ruby's `protected`.

hash_map.rb

# Say you're implementing a hash map, and you've got two
# sets of algorithms which are more efficient at
# different sizes:


class HashMap
  class << self
    def with_values(values)
      if values.size > 64
        LargeHashMap.new(values)
      else
        SmallHashMap.new(values)
      end
    end

    protected :new
  end

  class LargeHashMap < self
    # Efficient algorithms for large hash maps
  end

  class SmallHashMap < self
    # Efficient algorithms for small hash maps
  end
end


# If .new were private, the superclass's .with_values
# couldn't call it. Since it's protected, other objects
# can't call HashMap.new (or LargeHashMap.new).