Represent yes, no and absence

Learn

The values true and false represent yes-or-no results. A comparison such as tickets == 0 tests equality; tickets > 0 tests whether tickets is greater than zero. Each comparison produces a boolean that you can display with p.

nil commonly represents a missing or unknown value. It is a distinct value from false. Use p to make nil visible, and use value.nil? to test whether a value is nil. The question mark is part of this method name.

Ruby treats false and nil as false in truth tests, and every other value as true; this property is called truthiness. The ! operator negates that truthiness: !value is true for a false value and false for a true value. In particular, zero and an empty string are both truthy.

Example

tickets = 3
p tickets > 0
p tickets == 0
arrival = nil
p arrival
p arrival.nil?

Experiment

• Try Check available space

  Predict the comparisons, then run. Change booked to 10 and consider why equality and greater-than can give different answers.

• Try Inspect truthiness

  Predict the results of negating these four values, then run. Replace the empty string with "ready" and compare that line again.

Explore the official manual

• Official Ruby 4.0 documentation: Literals
• Official Ruby 4.0 documentation: Integer
• Official Ruby 4.0 documentation: NilClass
• Official Ruby 4.0 documentation: FalseClass
• Official Ruby 4.0 documentation: Control Expressions
• Official Ruby 4.0 documentation: BasicObject