------------------------------------------- Object#instance_variable_get
     obj.instance_variable_get(symbol)    => obj
------------------------------------------------------------------------
     Returns the value of the given instance variable, or nil if the
     instance variable is not set. The @ part of the variable name
     should be included for regular instance variables. Throws a
     NameError exception if the supplied symbol is not valid as an
     instance variable name.

        class Fred
          def initialize(p1, p2)
            @a, @b = p1, p2
          end
        end
        fred = Fred.new('cat', 99)
        fred.instance_variable_get(:@a)    #=> "cat"
        fred.instance_variable_get("@b")   #=> 99