Sinatra で Controller を分割したくなったら Rack::URLMap を使うとよさそう http://studio3104.hatenablog.com/entry/2014/10/03/013500

0_app.rb

require 'sinatra/base'

class Main < Sinatra::Base
  before do
    # nanka
  end

  get '/' do
    'index'
  end

  get '/foo' do
    'foo'
  end

  get '/bar' do
    'bar'
  end
end

0_config.ru

require 'sinatra'
require './app'
run Main

1_app.rb

require 'sinatra/base'

class Base < Sinatra::Base
  before do
    # nanka
  end
end

class Root < Base
  get '/' do
    'index'
  end
end

class Foo < Base
  get '/foo' do
    'foo'
  end
end

class Bar < Base
  get '/bar' do
    'bar'
  end
end

class Main < Sinatra::Base
  use Root
  use Foo
  use Bar
end

2_app.rb

require 'sinatra/base'

class Base < Sinatra::Base
  before do
    # nanka
  end
end

class Root < Base
  get '/' do
    'index'
  end
end

class Foo < Base
  get '/' do
    'foo'
  end
end

class Bar < Base
  get '/' do
    'bar'
  end
end

class Main < Sinatra::Base
  ROUTES = {
    '/' => Root,
    '/foo' => Foo,
    '/bar' => Bar,
  }
end

2_config.ru

require 'sinatra'
require './app'
run Rack::URLMap.new(Main::ROUTES)