representer.rb

class LazyRepresenter
  def initialize
    @getters = []
  end

  def call(object)
    @getters.reduce({}) do |hash, getter|
      hash.merge(getter.call(object))
    end
  end

  def represent(&getter)
    fail "No getter block provided!" unless block_given?
    @getters << getter
  end
end

# Przyklady:
id_and_name_representer = LazyRepresenter.new
  .represent do |object|
    { id: object.id }
  end
  .represent do |object|
    { name: object.name }
  end

lr.call(User.first)
lr.call(Event.first)

simple_tags_representation = lr.new.represent do |tag|
  {id: tag.id, name: tag.name}
end

some_group_presenter =
  V3::GroupRepresenter.new
    .basic
    .with_tags(simple_tags_representation)
    .with_participants
    .with_participants_count

group_presenter.call(some_group)