Why are my instance variables not existing across methods of the same class in ruby?

Why are my instance variables not existing across methods of the same
class in ruby?

I am doing the ruby koans and I am on the DiceSet project. I've made the
DiceSet class but my instance variables don't seem to persist with the
instance like I thought they would. My code is
class DiceSet
attr_reader :values
@values = []
puts @values.class
def roll(number_of_rolls)
(1..number_of_rolls).each do |roll|
puts @values.class
@values << (1..6).to_a.sample
end
return @values
end
end
The koan then uses my DiceSet class with
dice = DiceSet.new
dice.roll(5)
puts dice.values.class
assert dice.values.is?(Array)
I put the puts commands in there to follow whats happening with the
@values instance variable and only the first puts @values.class says its
an Array class. All the others are returning NilClass. Am I using instance
variables incorrectly or is there something else I am missing? Do instance
variables get deallocated after a method call?