Example uses of Object#tap that I really like

some_object_tap_uses.rb

# Logging some action in the console or log file
# Prevents lots of references to a variable
# Maybe not the best example, but potentially cleaner than the alternative
class ApplicationController
  after_filter :log_action_without_tap
  after_filter :log_action_with_tap
  private
    def log_action_with_tap
      "[ACTION LOG]: #{current_account.name} tried to #{action_name} #{controller_path}".tap{|l|
        l << flash.map{|k,v| "#{k}: #{v}"}.join(',') if flash.any?
        Rails.logger.info(l)
      }
    end
    # vs
    def log_action_without_tap
      action_to_log = "[ACTION LOG]: #{current_account.name} tried to #{action_name} #{controller_path} "
      if flash.any?
        action_to_log << " || "
        action_to_log << flash.map{|k,v| "#{k}: #{v}"}.join(',')
      end
      Rails.logger.debug(action_to_log)  
    end
end

# Debugging in a test
# No need to add a reference variable and new line to output
# to the console. Just tap it and call `puts` to see in the 
# test output.
class LoggerTest < ActiveSupport::TestCase
  def test_unknown_string_with_tap
    # Just remove the tap when done
    unknown_string.tap{|s| puts s}
  end
  
  def test_unknown_string_without_tap
    # lots of stuff to clean up after checking console output
    unknown_string = reference_to_output_being_tested
    puts unknown_string # uncomment this to see output
  end
end

# Use as a builder
# Allows for caching and simplifies 
# of a potentially complicated object definition
@routes ||= Routes.new.tap do |route|
  route.connect "some url", to: "SomeController#action"
  route.connect "some other url", to: "AnotherController#action"
end.finish_and_cache!