Is !object.nil? == object.present? in Rails?

Question

Is it safe to assume that !object.nil? == object.present? in Rails, or are there gotchas? Here's a scenario:

  def signed_in?
    !current_user.nil? # Would current_user.present? mean the same thing here?
  end

  def sign_in(user)
    cookies[:token] = user.token
    self.current_user = user
  end

  def current_user
    @current_user ||= User.find_by(token: cookies[:token]) if cookies[:token]
  end

Answer 1

.present? is the negation of .blank?, which is similar but decidedly unique from .nil?.

.nil? only evaluates whether an object is NilClass.

.blank? evaluates to true when evaluating a string that is not empty and may (or may not) contain whitespace.

It's superfluous to your question, but it's probably handy to note that .blank? and .present? are Rails methods, whereas .nil? is pure Ruby.

EDIT:

If, in your example, object is equal to false, then no, it's not safe to assume that !object.nil? == object.present?. However, if object is actually a Ruby/Rails object, then it's safe to assume that the statement will evaluate to true.

!false.nil? == false.present? #=> false

Answer 2

In rails generally I dont think so according to the docs here.

But the following should be true

!object.blank? == object.present?

In your case I think it should be true because of how the method current_user is defined.