class Rectangle
    attr_accessor :width
    attr_accessor :height
    attr_accessor :width2
    attr_accessor :height2

    def initialize(wdth, hgt)
        @width = wdth
        @height = hgt
    end

    def area()
        return @width * @height
    end

    def area2()
        return @width2 * @height2
    end

end

r = Rectangle.new(2,3)
r.width = 5    # give samename's variable value 给同名变量的变量赋值
r.height = 5
puts r.area()  # outputs is 25

r.width2 = 6   # not samename's variable create 无同名变量的变量创建
r.height2 = 6
puts r.area2() # outputs is 36

class Module
    def var( method_name )
        inst_variable_name = "@#{method_name}".to_sym    # .to_sym
        p inst_variable_name        #:=>:@bar

        define_method method_name do
            instance_variable_get inst_variable_name
        end

        define_method "#{method_name}=" do |new_value|
            instance_variable_set inst_variable_name, new_value
        end

    end
end

class Foo
    var :bar
end

f = Foo.new            # p f.bar
p f.class              #:=>Foo
p f.class.instance_methods(false)      #:=>["bar", "bar="]
f.bar = "good"                         #:=>"good" method bar=
p f.bar                                #:=>"good" method bar