flatten_with_dotted_keys.rb

class Hash
  def flatten_with_dotted_keys(&block)
    stack = []
    flattened = {}
    flatten_dfs(self, stack, flattened, block)
    flattened
  end

  private

  def flatten_dfs(elem, stack, flattened, block)
    case elem
    when Hash
      elem.each do |key, val|
        stack.push(key)
        flatten_dfs(val, stack, flattened, block)
        stack.pop
      end
    else
      flattened[stack.join('.')] = block.is_a?(Proc) ? block.call(elem) : elem
    end
  end
end

puts ({"foo" => "bar", "a"=>{"b"=>{"c"=>1}, "b2"=>{"c2"=> {"d2" => 2}}}}).flatten_with_dotted_keys.inspect
puts ({"foo" => "bar", "a"=>{"b"=>{"c"=>1}, "b2"=>{"c2"=> {"d2" => 2}}}}).flatten_with_dotted_keys { |e| e.to_s+"_suffix" }.inspect