unload/reload

rails-reload-example.rb

# Goal: put a non-Rails-aware Ruby library using normal `require`s in
# lib/mything. Have it transparently reloaded between requests like Rails app
# code is.
#
# The code here goes inside of your configure block in
# config/environments/development.rb. There are two parts, commented inline.

# Disable reload_classes_only_on_change. This makes Rails invoke the reloader
# even if no source files are changed. This is necessary because the autoloader
# and reloader don't know about our library, so they won't know to trigger a
# reload when they change. This will probably become slow for very large apps;
# on my (currently very small) app it costs about 85 ms in total request time.
config.reload_classes_only_on_change = false

# Manually unload and reload the library before every request. If it has global
# state, this will almost certainly fall over in terrible ways. If it defines
# constants other than the one ("Sim") explicitly dealt with here, you may
# actually die in real life. This assumes that there's a lib/sim.rb loading
# files from lib/sim/.
ActionDispatch::Reloader.to_prepare do
  # If the library's top level module is currently loaded, unload it
  if Object.const_defined?(:Sim)
    Object.send(:remove_const, :Sim)
  end

  # Instruct ruby to "unrequire" all of the gems files.
  # CAREFUL: make sure this only matches your library's files.
  sim_base = File.expand_path(File.join(File.dirname(__FILE__), '../../lib/sim'))
  $".delete_if do |s|
    is_in_sim_dir = s.start_with?(sim_base + "/")
    is_sim_file = s == sim_base + ".rb"
    is_in_sim_dir || is_sim_file
  end

  # Re-require your library
  # Note: because we removed all files previously required they will be reloaded
  # even if you didn't use load/autoload in your gem.
  require_relative "../../lib/sim"
end