1.CompositeLogger.cr

class CompositeLogger
  def initialize(@loggers : Array(Logger) = loggers)
  end

  macro method_missing(call)
    @loggers.each do |logger|
      logger.{{call}}
    end
  end
end

2.usage.cr

logger1 = Logger.new(File.open("debug.log", "w+")).tap(&.level = Logger::DEBUG)
logger2 = Logger.new(File.open("error.log", "w+")).tap(&.level = Logger::ERROR)
logger3 = Logger.new(STDOUT).tap(&.level = Logger::INFO)

logger = CompositeLogger.new([logger1, logger2, logger3])
logger.debug "Hi all!"
logger.info  "Hi stdout!"
logger.error "Hi stdout, error!"

# logger.debagu "..."  # gives a compile error

3.run.md

% crystal usage.cr
I, [2017-12-06 21:35:07 +0900 #8536]  INFO -- : Hi stdout!
E, [2017-12-06 21:35:07 +0900 #8536] ERROR -- : Hi stdout, error!

% cat debug.log
D, [2017-12-06 21:35:07 +0900 #8536] DEBUG -- : Hi all!
I, [2017-12-06 21:35:07 +0900 #8536]  INFO -- : Hi stdout!
E, [2017-12-06 21:35:07 +0900 #8536] ERROR -- : Hi stdout, error!

% cat error.log
E, [2017-12-06 21:35:07 +0900 #8536] ERROR -- : Hi stdout, error!