Question

I am new to Ruby and came across the defined? operator. I thought the ? implied that the method returned true/false but defined? returns a description of the identifier if it is defined.

I know that there is a true/false component in that the identifier is or is not defined but I thought that the ? meant that the return value always had to be true/false`. Help?

Answer 1

It returns a “truthy” value that is either “truthy-true” or “truthy-false”.

In Ruby, there are only two things that are truthy-false:

• false (the singleton object)
• nil (the singleton object)

Anything else is considered truthy-true. Tons of Ruby code leverages this fact for predicates. Checks for predicates, as such, should be:

if list.empty?

not:

if list.empty? == true