How to check if an instance variable is defined in a Ruby class


class Dog
  def initialize(name)
    @name = name

  def set_nickname(nickname)   #set with ruby_I don't use hoge, but this time I'll give it a try for simplicity!
    @nickname = nickname

  def print_nickname
    if !defined?(@nickname)
      puts('Not Set')

If it is nil when you refer to if @age, you don't know which of the following cases.

-Is it nil because it has never been defined? --Is it the result of assigning @nickname = nil once?

In such a case, you should use defind? (@Age).

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