Question

There seem to be a mistake in my code. However I just can’t find it out.

class Class
def attr_accessor_with_history(attr_name)
  attr_name = attr_name.to_s

  attr_reader attr_name
  attr_writer attr_name

  attr_reader attr_name + "_history"
  class_eval %Q{
   @#{attr_name}_history=[1,2,3]
  }

end
end

class Foo
 attr_accessor_with_history :bar
end

f = Foo.new
f.bar = 1
f.bar = 2
puts f.bar_history.to_s

I would expect it to return an array [1,2,3]. However, it doesn’t return anything.

Answer 1

You will find a solution for your problem in Sergios answer. Here an explanation, what’s going wrong in your code.

With

class_eval %Q{
 @#{attr_name}_history=[1,2,3]
}

you execute

 @bar_history = [1,2,3]

You execute this on class level, not in object level.
The variable @bar_history is not available in a Foo-object, but in the Foo-class.

With

puts f.bar_history.to_s

you access the -never on object level defined- attribute @bar_history.

When you define a reader on class level, you have access to your variable:

class << Foo 
  attr_reader :bar_history
end
p Foo.bar_history  #-> [1, 2, 3]