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

Question

In Sinatra, I\'m unable to create global variables which are assigned values only once in the application lifetime. Am I missing something? My simplified code looks like thi

Answer 1

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'
    end
end

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

# File 'lib/sinatra/base.rb', line 877

def 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.

Answer 2

You could use OpenStruct.

require 'rubygems'
require 'sinatra'
require 'ostruct'

configure do
  Struct = OpenStruct.new(
    :foo => 'bar'
  )
end

get '/' do
  "#{Struct.foo}" # => bar
end

You can even use the Struct class in views and other loaded files.

Answer 3

Another option:

helpers do

  def a
   a ||= 1
  end

end

Answer 4

class WebApp < Sinatra::Base
  configure do
    set :my_config_property, 'hello world'
  end

  get '/' do
    "#{settings.my_config_property}"
  end
end

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).