Question

After studying ruby for about a month, I decided to move on to Sinatra. I need help understanding a Sinatra snippet which illustrates conditions and routing. Could someone clearly explain what’s going on line-by-line and how this block is actually randomizing the route?

set(:probability) { |value| condition { rand <= value } }

  get '/win_a_car', :probability => 0.1 do
    "You won!"
  end

  get '/win_a_car' do
    "Sorry, you lost."
  end

Answer 1

The overall behavior of this will cause the first route to be loaded about 10% of the time and the 2nd route will be loaded the rest of the time.

The first route uses a condition set via probability. probability set above will pass its value and test to see if a random # between 0-1 is less than this probability value. Since the value is 0.1, it will return true 10% of the time.

The other 90% of the time the 2nd route will be called. The earlier routes take preference, the first valid route found will be called.

If you wanted to set the probability in another setting, you would need to defer the evaluation of the probability with a Proc.

Read more on conditional routes here:
http://www.sinatrarb.com/intro#Conditions