Making an equals method without needing to make private fields public

Question

I'm writing a Ruby class, and want to override the == method. I want to say something like:

class ReminderTimingInfo
   attr_reader :times, :frequencies #don't want these to exist

   def initialize(times, frequencies)
      @times, @frequencies = times, frequencies
   end

   ...

   def ==(other)
      @times == other.times and @frequencies == other.frequencies
   end
end

How can I do this without making both times and frequencies publicly viewable?

FOLLOW UP:

class ReminderTimingInfo

  def initialize(times, frequencies)
    @date_times, @frequencies = times, frequencies
  end

  ...

  def ==(other)
    @date_times == other.times and @frequencies == other.frequencies
  end

  protected

  attr_reader :date_times, :frequencies
end

didn't mean to upvote your comment, hehe. I'd say getters are something to be avoided at all costs. It would be nice if there were some form of protected access or something...Hmmm maybe there is. — Alex Baranosky, Aug 06 '10 at 00:25
Object state should be as private as possible. Anything the class user doesn't need to make a command to the object should be invisible to the user. — Alex Baranosky, Aug 06 '10 at 00:26

Zargony · Accepted Answer · 2010-08-06T00:49:03.957

4

If you set times and frequencies accessors to protected, they'll be only accessible from instances of that class and descendants (which should be ok, since descendants can access the instance variables anyway and should know how to handle it correctly).

class ReminderTimingInfo

  # …

protected
  attr_reader :times, :frequencies

end

edited Aug 06 '10 at 00:49

answered Aug 06 '10 at 00:27

Zargony

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thanks... that makes sense. I chose to implement it slightly different... see above :) – Alex Baranosky Aug 06 '10 at 00:35
You're right. It's doing the same, but looks nicer, especially with many attributes (less duplication). – Zargony Aug 06 '10 at 00:51

score 2 · Answer 2 · answered Aug 07 '10 at 07:55

2

You could do

  def ==(other)
    @date_times == other.instance_eval{@date_times} and @frequencies == other.instance_eval{@frequencies}
  end

But somehow I suspect that that's missing the point!

answered Aug 07 '10 at 07:55

Andrew Grimm

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Making an equals method without needing to make private fields public

2 Answers2