How to split a class into multiple files in Ruby?

Question

ruby

I understand with Grape and formed for myself an application structure similar to that described here ( repository ), only without using Rails. It turned out the following:

app/api/v1.rb
app/api/v1/product.rb
app/api/v1/review.rb

app/api/v1.rb :

module API
  class V1 < Grape::API
    version 'v1', using: :path
    content_type :json, 'application/json; charset=UTF-8'
    prefix :api
    format :json

    before do
      header['Access-Control-Allow-Origin'] = '*'
      header['Access-Control-Request-Method'] = '*'
    end

    mount Product
    mount Review
  end
end

app/api/v1/product.rb :

module API
  class V1::Product < Grape::API
    resource :products do
      get do
        %w(Cofee Tea Rice Meat)
      end
    end
  end
end

app/api/v1/review.rb :

module API
  class V1::Review < Grape::API
    resource :reviews do
      get do
        "This is review"
      end
    end
  end
end

There is environment.rb , which requests all the necessary files before starting the application. If I first request app/api/v1.rb , then the error is uninitialized constant API::V1::Product . If you first request one of the files in the subdirectory - uninitialized constant API::V1 . In principle, this is all logical and understandable.
Of course, you can declare a Product and Review prototype and request app/api/v1.rb first . Or, first request files in the subdirectory, and make them look like

module API
  class V1 < Grape::API
    class Product < Grape::API
      ...
    end
  end
end

Is it possible to leave the structure and code, while getting rid of errors? After all, in the application I cited at the beginning of the question, exactly the same structure is used and it all works.