code.rb

require 'json'

class JSONSerializer
  def self.deserialize(json, cls)
    obj = cls.new()
    parsed = JSON.parse(json)
    parsed.each do |child|
      prop = child[0]
      value = child[1]
      obj.send("#{prop}=", value)
    end
    obj
  end
end

class JSONModel
  attr_accessor :data

  def initialize
    @data = {}
  end

  def method_missing(name, *arguments)
    value = arguments[0]
    name = name.to_s

    #puts "method_missing '#{name}', '#{name[-1, 1]}'"

    # if the method's name ends with '='
    if name[-1, 1] == "="

      method_name = name[0..-2]
      #puts "Setting '#{method_name}' to '#{value}'"
      @data[method_name] = value

    else

      #puts "Getting '#{name}'"
      @data[name]

    end
  end
end

class Account < JSONModel
end

class Entity < JSONModel
end

str = '{"id": 1, "firstName": "Chris", "lastName": "Roberson"}'

account = JSONSerializer.deserialize(str, Account)
puts account.class
puts "#{account.firstName} #{account.lastName}"

entity = JSONSerializer.deserialize(str, Entity)
puts entity.class
puts "#{entity.firstName} #{entity.lastName}"