Why this instance variable is not incrementing? - ruby

Question

This short code is working when I'm using class variable ##points instead of #points. I wonder why it's happening like this? Someone can explain me? It looks like #points is always nil.
class Game
#points = 0
def start
until #points == 10
puts "Guess number between 0 and 10:"
num = gets.chomp.to_i
break if #points == 0
guess_number(num)
puts "Your score is: #{#points}"
end
end
def guess_number(num)
#points += 1 if num == rand(0..10)
end
end
game = Game.new
game.start

Answer 1

Because #points is a class instance variable, and to access it from within the instance method's scope you'd have to either do
self.class.instance_variable_get(:#points)
or define an attr_accessor in Game's singleton_class
class Game; class << self; attr_accessor :points; end; end
and then you'd be able to do
self.class.points
But neither of these is what you really want.
code is working when I'm using class variable ##points instead of
#points
It is working, because you do have access to class variable from within a scope of an instance methods.
It looks like #points is always nil
It is always nil, because you never defined an instance variable #points, but, as said, class instance variable.
So these three things are different (you could read up something about Ruby scoping - do not mix with AR scopes):
class variable
class instance variable
instance variable
To solve it there are many ways, but if you want to keep it on the instance level, wrap #points into a method:
def points
#points ||= 0
end
And then use it as points - now it'll work as you are expecting.

Answer 2

Thanks to answer by Andrey Deineko. I came up with such solution to use instance variable here.
class Game
def initialize
#points = 0
end
def start
until points == 10
puts "Guess number between 0 and 10:"
num = gets.chomp.to_i
break if points == 10
guess_number(num)
puts "Your score is: #{points}"
end
end
private
def guess_number(num)
if num == rand(0..10)
increment_points
end
end
def points
#points
end
def increment_points
#points += 1
end
end
game = Game.new
game.start