CODEWITHSUNDEEP
ruby
Graham Slick
Graham Slick

Reputation: 6870

Variable assignment inside of ruby methods

I have this pretty simple method:

def update_context(msg, session, sender)
    previous_context = session.context 
    session.update(context: intent_determination(msg, session.context, sender))
    session.update(context: brand_determination(msg, session.context))
    session.update(context: style_determination(msg, session.context))
    session.update(context: price_range_determination(msg, session.context))
    session.update(context: size_determination(msg, session.context))
       p previous_context
       p session.context
       p (previous_context == session.context)
    unless session.context.size == 0
      if previous_context == session.context
        session.context["intent"] = "lost"
        session.save
      end
    end
  end

My problem is certainly due to a stupid mistake I can't see but please bear with me on this one, I really can't see it.

As you can see, I "save" the session's context in a previous_context variable at the beginning of the method. Then, I'm running a few updates on the context. However, when I print previous_context, session.context and previous_context == session.context, I get the same result for the first two, and true for the last one.

How is this possible ? I assigned to previous_context the value of session.context before updating it. And then, previous_context has the same value as session.context after I've updated it.

I really can't see where I screwed up here, or there is definitely something I don't understand.

Upvotes: 0

Views: 56

Answers (2)

Hilario Fernandes
Hilario Fernandes

Reputation: 199

in Ruby, variables are just references to objects, so what you are doing there is merely creating a new reference to the same object. If you wish to save the previous state you will have to copy the entire object.

See this answer for a more graphic explanation.

Upvotes: 0

Tommy Steimel
Tommy Steimel

Reputation: 791

previous_context = session.context makes the previous_context variable point to the same object as session.context. If you want to change one without affecting the other, you'll need to create a copy of session.context to store in previous_context.

Upvotes: 1

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