Ruby: “if !object.nil?” or “if object”

Question

Are they the same when used in an if/else/end statement? What do you usually do? I\'m wondering if there are any subtle differences or edge cases where ob

Answer 1

Objects can override nil? but they cannot be falsely unless they are nil or false. Personally I use nil? or ActiveSupport's present? so that I maintain that flexibility. I also think it reads a bit better.

Answer 2

if object tests if object isn't either nil or false.

!object.nil? tests if object isn't nil. (Rubydoc)

So when object is false, they have different values.

Answer 3

There is one and only one case in which !object.nil? and object evaluate to different results in a boolean context and that is if object is false. In all other situations the result is the same.

With this, I think we can answer your real question (which is: Is there any situation where I must use if !object.nil? instead of just if object when protecting against object being nil?):

No, you can always use if object if you want to check against nil.

Answer 4

Well. if object will behave differently from if !object.nil? if object=false.

That's about it.

Answer 5

There are differences. For example:

false.nil?
# => false

So:

if !false.nil?
  'foo'
end
# => "foo"

if false
  'foo'
end
# => nil

As @tokland suggested, in most cases using !obj.nil? construction is unnecessary.