A Decorator module for Trailblazer, basically it's just a copy of the Representer module, but it only adds the rendering methods.

decorator.rb

# Including this will change the way the Operation renders the contract
#
# TODO: so far, we only support JSON, but it's two lines to change to support any kind of format.
module Trailblazer::Operation::Decorator
  def self.included(base)
    base.inheritable_attr :_decorator_class
    base.extend ClassMethods
  end

  module ClassMethods
    def decorator(constant=nil, &block)
      return decorator_class unless constant or block_given?

      self.decorator_class= Class.new(constant) if constant
      decorator_class.class_eval(&block) if block_given?
    end

    def decorator_class
      self._decorator_class ||= infer_decorator_class
    end

    def decorator_class=(constant)
      self._decorator_class = constant
    end

    def infer_decorator_class
      Disposable::Twin::Schema.from(contract_class,
        include:          [Representable::JSON],
        superclass:       Representable::Decorator,
        representer_from: lambda { |inline| inline.representer_class },
      )
    end
  end

private
  module Rendering
    def to_json(*)
      self.class.decorator_class.new(decorated).to_json
    end

    def decorated
      contract
    end
  end
  include Rendering

end