Converts a hash to an OpenStruct along with all its nested hashes. The hash and all its sub-hashes become OpenStruct instances in the resulting structure.

hash_to_ostruct.rb

require 'ostruct'

class OpenStruct
  def self_and_field_pairs
    each_pair.map { |field, _| [self, field] }
  end
end

class Hash
  # Converts a hash to an OpenStruct along with all its nested hashes. The hash
  # and all its sub-hashes become OpenStruct instances in the resulting
  # structure.
  def to_ostruct
    top_ostruct = OpenStruct.new(self)
    stack = top_ostruct.self_and_field_pairs
    until stack.empty?
      ostruct, field = stack.pop
      case value = ostruct[field]
        when Hash
          ostruct[field] = sub_ostruct = OpenStruct.new(value)
          stack += sub_ostruct.self_and_field_pairs
        when Array
          # When the field is an array, iterate through all its elements
          # replacing all hashes with OpenStruct instances and push the new
          # structure's fields to the stack for nested inspection of hashes
          # later.
          value.each_with_index do |element, index|
            case element
              when Hash
                value[index] = sub_ostruct = OpenStruct.new(element)
                stack += sub_ostruct.self_and_field_pairs
            end
          end
      end
    end
    top_ostruct
  end
end

hash_to_ostruct_test.rb

require 'minitest/autorun'
require_relative 'hash_to_ostruct'

class HashToOpenStructTest < Minitest::Test
  def test_hash_to_ostruct
    hash = {
        alpha: 1,
        bravo: 2,
        charlie: 3,
        delta: {
            delta_1: {
                xray: 'string1',
                yankee: 'string2',
                zulu: 'string3'
            },
            delta_2: [
                :romeo,
                :oscar,
                {
                    yankee: 1.23
                }
            ]
        }
    }
    ostruct = hash.to_ostruct
    assert_equal 1, ostruct.alpha
    assert_equal 2, ostruct.bravo
    assert_equal 3, ostruct.charlie
    assert_equal 'string1', ostruct.delta.delta_1.xray
    assert_equal 'string2', ostruct.delta.delta_1.yankee
    assert_equal 'string3', ostruct.delta.delta_1.zulu
    assert_includes ostruct.delta.delta_2, :romeo
    assert_includes ostruct.delta.delta_2, :oscar
    assert_equal 1.23, ostruct.delta.delta_2[2].yankee
  end
end