Awesome Ruby feature. Do not use it in real projects!

super_logger.rb

require 'logger'

class SuperLogger
  include Logger::Severity
  attr_accessor :level

  def initialize(level = INFO)
    @level = level || INFO
  end

  def log?(severity)
    @level <= severity
  end

  def log(message = nil, severity = INFO, _ = (log?(severity) ? message ||= yield : message = nil))
    puts message if message
  end
end

# Let's try this
logger = SuperLogger.new
logger.log('message info')
logger.log('message debug', Logger::DEBUG)
logger.log { 'block info' }
logger.log('message and block info') { sleep(10); 'block info - never called' }
logger.log(nil, Logger::DEBUG) { sleep(10); 'block debug - never called' }