NullObject logger

gistfile1.rb

Purchase = Struct.new(:description, :price)

DATA = [
  Purchase.new("Walkman", "1.25"),
  Purchase.new("Mini-disc player", "2.57"),
  Purchase.new("Record player", "3.54")
]

require 'logger'

class TransactionImport
  attr_reader :data, :logger

  def initialize(data, options = {})
    @data   = data
    @logger = options.fetch(:logger) { default_logger }
  end

  def import
    data.each do |record|
      # ...do import work
      logger.info("Processing #{record.description}")
    end
  end

  private

  def default_logger
    @logger ||= Logger.new(STDOUT)
  end
end

class FabulousLogger
  def info(log_message)
    puts ">>> #{log_message} <<<"
  end
end

class NullObject < BasicObject
  def method_missing(*)
  end

  def respond_to_missing?(name)
    true
  end
end

# Normal logger
TransactionImport.new(DATA).import

# An alternative logger
TransactionImport.new(DATA, logger: FabulousLogger.new).import

# No logging using `NullObject`
TransactionImport.new(DATA, logger: NullObject.new).import