Boolean methods in ruby

In this article, we’ll look at what boolean methods are and how they work.

This article is divided into the following sections:

1. What are Boolean methods in ruby
2. The question mark is used when the method returns boolean value
3. Perfectly combined with comparison operators
4. Conclusions

What are Boolean methods in ruby

Methods that end with the question mark (?) in ruby has a few names: predicates, query or boolean methods. It’s assumed that by these methods we ask a certain question and can get certain information about the object. For example, ruby has the method ‘any?’. With it, we can ask an array if it has any elements inside it and as a result, we will get ‘true’ or ‘false’.

puts [].any? 
puts ["element one", "element two", "element three"].any?

produces:

false
true
=> nil

More examples:

irb(main):078:0* "daadsasd".is_a?(String)
=> true
irb(main):079:0> "daadsasd".tainted?
=> false
irb(main):080:0> "daadsasd".nil?
=> false
irb(main):081:0> "daadsasd".respond_to?("downcase!")
=> true

The question mark is used when the method returns boolean value

From the previous examples, it’s obvious that the question mark (?) at the end of the method is set when we have a method that returns boolean value — ‘true’ or ‘false’.

Perfectly combined with comparison operators

Since comparison methods typically return either true or false, they are perfectly matched to the concept of Boolean methods.

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For instance:

def even?(x)
  (x % 2) == 0 
end
def more_then_five?(x)
  x > 5 
end 
def less_then_three?(x)
  x < 3 
end 
puts even?(2)
puts even?(3)
puts more_then_five?(3)
puts more_then_five?(6)
puts less_then_three?(2)
puts less_then_three?(4)

produces:

true
false
false
true
true
false
=> nil

Conclusions

— Methods that end with the question mark (?) are called boolean methods;
— Boolean methods must return true or false;
— Boolean methods are ideally combined with comparison operators.

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