How to use Proc.new

Question

I was curious about this line:

set :views, Proc.new

What it do, and why is Proc.new used?

class ApplicationController < Sinatra::Base
  configure do
    set :views, Proc.new { File.join(root, "../views/") }
    enable :sessions unless test?
    set :session_secret, "secret"
  end
end

Answer 1

This proc is not a static thing, it takes a settings value root and evaluates a path to views. Here is a piece of documentation of Sinatra:

When the setting value is a Proc , evaluation is performed every time the setting is read so that other settings may be used to calculate the value

Once you set root value you don't need to set the full path for views.