How to turn a config.ru file into a single Rack application?

I have a config.ru file that is starting to have duplicate code:

map '/route1' do
  run SampleApp.new
end

map '/route2' do
  run SampleApp.new
end

I would like to turn this config.ru file into its own Rack application so that all I have to do is:

map '/' do
  run MyApp.new
end

What is the correct way to create your own Rack application? Specifically, how can I create a class so that I can use the map method within my class to define a bunch of routes?

Solution:

Here is a working solution:

class MyApp

  def initialize
    @app = Rack::Builder.new do
      # copy contents of your config.ru into this block
      map '/route1' do
        run SampleApp.new
      end

      map '/route2' do
        run SampleApp.new
      end
    end
  end

  def call(env)
    @app.call(env)
  end
end

I tried this before, but couldn't get it to work because I was trying to pass instance variables to the map blocks. For example:

def initialize
  @sample_app = SampleApp.new
  @app = Rack::Builder.new do
    map '/route1' do
      run @sample_app   # will not work
    end
  end
end

The reason this will not work is because the block being passed to map is being evaluated in the context of a Rack::Builder instance.

However, it will work if I pass a local variable:

def initialize
  sample_app = SampleApp.new
  @app = Rack::Builder.new do
    map '/route1' do
      run sample_app   # will work
    end
  end
end