Recursively symbolize ruby hash keys in a nested structure. Uses refinements instead of monkey patching Hash.

stringify_recursive.rb

# # usage:
# require_relative 'lib/stringify_helper'
# extend StringifyHelper
# using StringifyHelper
#
# { test: { foo: "bar" } }.deep_stringify_keys #=> \
# #  { "test" => { "foo" => "bar" } } 

module StringifyHelper
  extend self

  def stringify_recursive(hash)
    {}.tap do |h|
      hash.transform_keys(&:to_s).each do |key, value|
        value = case value
        when Hash   then stringify_recursive value
        when Array  then value.map { |elem| elem.is_a?(Hash) ? stringify_recursive(elem) : elem }
        else
          value
        end
        h[key] = value
      end
    end
  end

  refine Hash do
    def deep_stringify_keys
      StringifyHelper.stringify_recursive self
    end
  end
end