Question

I am using the authlogic gem with Ruby on Rails, and I have been using the following to obtain the id of the user that is currently logged in:

current_user = UserSession.find
id = current_user && current_user.record.id

I’m not understanding how current_user && current_user.record.id returns the current user id. I would think this would return a boolean. Can someone explain how this works?

Answer 1

The logical and is short circuiting. That means that if the construct is X && Y, and X is false then Y never gets checked because the whole thing is certainly going to be yield false.

That code is saying, essentially:

if (current_user is TRUE) {
    id = current_user.record.id;
]

Here’s some console output showing you get the second value if the first is true:

irb(main):005:0> true && 9
=> 9

and nil if the first is nil:

irb(main):008:0> nil && 9
=> nil