In Sinatra(Ruby), how should I create global variables which are assigned values only once in the application lifetime?

class WebApp < Sinatra::Base  configure do    set :my_config_property, 'hello world'  end  get '/' do    "#{settings.my_config_property}"  endend

Beware that if you use Shotgun, or some other Rack runner tool that reloads the code on each request the value will be recreated each time and it will look as if it's not assigned only once. Run in production mode to disable reloading and you will see that it's only assigned on the first request (you can do this with for example rackup --env production config.ru).

I ran into a similar issue, I was trying to initialize an instance variable @a using the initialize method but kept receiving an exception every time:

class MyApp < Sinatra::Application    def initialize        @a = 1    end    get '/' do        puts @a        'inside get'    endend

I finally decided to look into the Sinatra code for initialize:

# File 'lib/sinatra/base.rb', line 877def initialize(app = nil)  super()  @app = app  @template_cache = Tilt::Cache.new  yield self if block_given?end

Looks like it does some necessary bootstrapping and I needed to call super().

    def initialize        super()        @a = 1    end

This seemed to fix my issue and everything worked as expected.

Another option:

helpers do  def a   a ||= 1  endend