snippet.rb

class Hash
  # Flattens a hash by joining keys with joiner. Meant for use with String or
  # Symbol keys. Resulting hash keys take on the type of the parent key.
  #
  #  { 'a' => { 'b' => 1 } }.flatten_with_joined_keys
  #  # => {"a_b"=>1}
  #  { :a => { :b => { :c => { :d => 1 } } } }.flatten_with_joined_keys('')
  #  # => {:abcd=>1}
  def flatten_with_joined_keys(joiner = '_')
    output = {}
    each do |parent_key, parent_value|
      if parent_value.is_a?(Hash)
        parent_value.each do |child_key, child_value|
          new_key = "#{parent_key}#{joiner}#{child_key}"
          new_key = new_key.to_sym if parent_key.is_a?(Symbol)
          output[new_key] = child_value
        end
      else
        output[parent_key] = parent_value
      end
    end
    if output.values.detect { |v| v.is_a?(Hash) }
      output.flatten_with_joined_keys(joiner)
    else
      output
    end
  end
end