Question

I have been trying to get the hang of metaprogramming in ruby by reading other people’s code on the same. I have this piece of code that is probably too cryptic for me to debug. Here is the code.

#!/usr/bin/env ruby

class Person

  def print_name
    p "#{Person.identity.name}"
  end

  class << self
    attr_accessor :identity

    def identify()
      self.identity ||= Identity.new
      yield(identity)
    end
  end

  class Identity
    attr_accessor :name

    def initialize
      @name = "kibet"
    end
  end
end

me = Person.new
me.print_name

And the error I’m getting is this

`print_name': undefined method `name' for nil:NilClass (NoMethodError)
    from ./meta_config.rb:28

Help’s highly appreciated.

Answer 1

I vaguely understood what you were trying to do there.. Check this out

class Person

  def print_name
    p "#{Person.identity.name}"
  end

  class << self
    attr_accessor :identity

    def identity
      @identity || Identity.new
    end
  end

  class Identity
    attr_accessor :name

    def initialize
      @name = "kibet"
    end
  end
end

me = Person.new
me.print_name

Things to note:

• I guess the method name was a typo. U meant identity intead of identify and please get rid of the braces. This is ruby 🙂
• calling self.identity inside will cause a stackoverflow. hence, directly access the value of instance variable
• I still could not understand why you need a yield there, when you would never pass a block.