ruby - Making a class instance variable unwritable from outside world -

class event      @event_list = {}      attr_reader :name, :value      def initialize(name, value)       @name  = name       @value = value     end      def to_s       "#{@value}"     end      class << self        def event_list           @event_list       end        def event_list=(value); end        def register_event(name, value)           @event_list[name] = event.new(name, value)       end        def registered_events           event_list       end     end end 

in above code snippet can access @event_list using event.event_list, interesting thing able modify variable outside

event.event_list[:name] = "hello" event.event_list  # => { :name => 'hello' } 

how can avoid ?, don't want modify @event_list outside.

as far know, can't stop outside code modifying instance variables in ruby. if don't use attr_reader , attr_writer can still accessed using object#instance_variable_set. ruby doesn't have private variables (or constants), variables politely asked not modify.

if don't define event_list=, seen indication @event_list private variable. solution problem.

then there problem mutable objects. since objects in ruby sadly mutable, if can reference object can change it.

this can solved object#freeze stops object being modified. unfortunately means not can modify it.

ruby not locking things down. openness core part of language need learn work with.