问题:

As Ruby 2.3 introduces the Safe navigation operator(&.), a.k.a lonely operator, the behavior on nil object seems odd.

nil.nil?    # => true
nil&.nil?   # => nil

Is that designed to behave like this way? Or some edge case that slipped away when adding the lonely operator?

回答1:

foo&.bar is shorthand for foo && foo.bar, so what would you expect the result of the expression nil && nil.nil? to be?

回答2:

This is because nil&.nil? is shorthand for nil && nil.nil?. This would evaluate to nil && true, which is then nil.

(nil && x).nil? always evaluates to true, for any value of x.

While the syntax has power, this specific case has some potential to become a 'gotcha' for a developer:

(stuff&.things).nil? => This produces true if stuff doesn't exist, or stuff.things returns nil.

vs. the below case:

stuff&.things&.nil? => This produces nil in every case except the case where stuff.things returns something other than nil, in which case it would return false.

Because of the difficulty in normal boolean logic of differentiating between false and nil, it is unlikely that this would make sense in normal logic.