better JSON serializer that returns an object with pre-defined attribute readers

object_mapper.rb

require 'json'
require 'securerandom'
require 'delegate'

class ObjectMapper < SimpleDelegator
  def self.parse(json_string, **opts)
    JSON.parse(json_string, object_class: JsonHash, create_additions: true, create_id: JSON_CREADE_ID, **opts)
  end

  JSON_CREADE_ID = SecureRandom.uuid.freeze

  alias parser __getobj__

  def new(source, opts = {})
    parser.new(source, object_class: JsonHash, create_additions: true, create_id: JSON_CREADE_ID, **opts)
  end

  class JsonHash < Hash
    def [](key)
      key == JSON_CREADE_ID ? JsonStruct : super
    end
  end

  class JsonStruct
    STRUCT_CACHE = Hash.new do |hash, key|
      hash[key] = Struct.new(*key, keyword_init: true)
    end

    def self.json_creatable?
      true
    end

    def self.json_create(result)
      symbolized_result = result.transform_keys(&:to_sym)
      STRUCT_CACHE[symbolized_result.keys].new(symbolized_result).freeze
    end
  end

  private_constant :JsonHash, :JsonStruct
end

# Replace the default JSON parser:
JSON.parser = ObjectMapper.new(JSON.parser)

parsed = JSON.parse(<<-JSON)
  {
    "obj": {
      "nested": 1
    }
  }
JSON

if parsed.obj.nested == 1
  puts "success!"
else
  raise "failed!" 
end

# or call the ObjectMapper.parse method directly:
parsed = ObjectMapper.parse(<<-JSON)
  {
    "obj": {
      "nested": 1
    }
  }
JSON

if parsed.obj.nested == 1
  puts "success!"
else
  raise "failed!" 
end