Ruby on Rails temporary instance variable - ruby-on-rails

Question

I want to use an instance variable throughout a class's methods. Unfortunately, the methods are all class (not instance) methods, so the classic #my_data ||= [1,2,3] doesn't work, since every call to the class's class-methods will reuse the same data forever:
class MyThing
class << self
def do_something
do_something_else
end
private
def my_data
#my_data ||= Time.now
end
def do_something_else
puts my_data
end
end
end
MyThing.do_something # puts the current time
MyThing.do_something # puts the same time as above (not what I want)
One way around it is to declare the variable, then set it to nil at the end of the method like this:
class MyThing
class << self
def do_something
#my_data = my_data
do_something_else
#my_data = nil
end
private
def my_data
Time.now
end
def do_something_else
puts #my_data || my_data
end
end
end
MyThing.do_something # puts the current time
MyThing.do_something # puts the new current time (yay)
However, setting the data and destroying it at the start and end of the method seems messy.
Is there a cleaner way to say "set (#my_data = Time.now) until the end of this method"?

Answer 1

It's soluiton, if I understand you correctly.
class MyThing
class << self
def do_something
do_something_else
end
private
def my_data
#my_data = Time.now
end
def do_something_else
puts my_data
end
end
end

Answer 2

The name says it all "instance variable" is available as long as the instance lives. In your case that instance is the MyThing class, meaning it doesn't reset automatically. Classes stay loaded as long as your program runs, so it will never reset.
The simplest solution for the given scenario is to use method arguments.
class MyThing
class << self
def do_something
do_something_else(my_data)
end
private
def do_something_else(my_data)
puts my_data || Time.now
end
end
end
The other option you already discovered, that is, setting an instance variable and then resetting it.
Another alternative is moving the thing your doing into an class instance. The disadvantage here is that this solution produces more overhead code. However it does keep the MyThing class cleaner, since you can move helper methods into this new class.
class MyThing
class DataObject
attr_reader :data
def initialize(data)
#data = data || Time.now
end
def do_something_else
puts data
end
end
class << self
def do_something
DataObject.new(my_data).do_something_else
end
end
end
If possible you could also create a MyThing instance instead of an DataObject instance, but I assumed the MyThing class already has another purpose.