比较下面两段代码:问题传递红宝石
class Logger
def self.add_logging(id_string)
define_method(:log) do |msg|
now = Time.now.strftime("%H:%M:%S")
STDERR.puts "#{now}-#{id_string}: #{self} (#{msg})"
end
end
end
class Song < Logger
add_logging "Tune"
end
song = Song.new
song.log("rock on")
class Logger
def self.add_logging(id_string)
def log(msg)
now = Time.now.strftime("%m")
puts "#{now}-#{id_string}: #{self}(#{msg})"
end
end
end
class Song < Logger
add_logging "Tune"
end
s = Song.new
s.log("can't smile with you")
#=> NameError: undefined local variable or method `id_string' for #<Song:0x000001018aad70>
我想不通为什么第二种情况下得到NameError错误,为什么ID_STRING可以”不会传递给它。