If a class exists, then use it. If not, then create the class as a child class of OpenStruct

example.rb

# ActiveSupport is loaded

items = [
  {type: 'post', a: 'a', b: 'b', c: 'c'},
  {type: 'resource', b: 'c', c: 'd', d: 'b'}
  {type: 'resource', c: 'b', b: 'c', a: 'a'}
]

def transform_hash(hsh)
  if hsh.key?(:type)
    singular_name = hsh[:type].singularize.titleize
    klass_name = "WordpressApiRuby::#{singular_name}"
    if Object.const_defined?("WordpressApiRuby::#{singular_name}")
      klass = klass_name.constantize
    else
      klass = Object.const_set klass_name, Class.new(OpenStruct)
    end
    klass.new(hsh)
  else
    OpenStruct.new(hsh)
  end
rescue => e
  # #<NameError: wrong constant name WordpressApiRuby::Resource>
  binding.pry
end

items.map do |item|
  transform_hash(item)
end