When do Ruby instance variables get set?

Question

class Hello
@hello = \"hello\"
    def display
        puts @hello
    end
end

h = Hello.new
h.display

I created the class above. It doesn\'t prin

Answer 1

there is a clear description in the book "The ruby programming language", read it will be very helpful. I paste it here(from chapter 7.1.16):

An instance variable used inside a class definition but outside an instance method definition is a class instance variable.

class Point
    # Initialize our class instance variables in the class definition itself
    @n = 0              # How many points have been created
    @totalX = 0         # The sum of all X coordinates
    @totalY = 0         # The sum of all Y coordinates

    def initialize(x,y) # Initialize method 
      @x,@y = x, y      # Sets initial values for instance variables
    end

    def self.new(x,y)   # Class method to create new Point objects
      # Use the class instance variables in this class method to collect data
      @n += 1           # Keep track of how many Points have been created
      @totalX += x      # Add these coordinates to the totals
      @totalY += y

      super             # Invoke the real definition of new to create a Point
                    # More about super later in the chapter
    end

    # A class method to report the data we collected
    def self.report
        # Here we use the class instance variables in a class method
        puts "Number of points created: #@n"
        puts "Average X coordinate: #{@totalX.to_f/@n}"
        puts "Average Y coordinate: #{@totalY.to_f/@n}"
    end
end

......

Because class instance variables are just instance variables of class objects, we can use attr, attr_reader, and attr_accessor to create accessor methods for them.

class << self
  attr_accessor :n, :totalX, :totalY
end

With these accessors defined, we can refer to our raw data as Point.n, Point.totalX, and Point.totalY.