Predicate methods (ending with ?) in Ruby

Introduction

Predicate methods help you check if something is true or false in a simple way. They make your code easier to read and understand.

When you want to check if a number is even or odd.

When you want to see if a string is empty.

When you want to find out if an object is nil (nothing).

When you want to check if a file exists.

When you want to test if a condition is true or false before doing something.

Syntax

Ruby

def method_name?
  # return true or false
end

Predicate methods always end with a question mark ?.

They return true or false to answer yes/no questions.

Examples

This method checks if a number is even. It returns true if yes, false if no.

Ruby

def even?(number)
  number % 2 == 0
end

The empty? method checks if a string has no characters.

Ruby

"hello".empty? # returns false
"".empty?      # returns true

The nil? method checks if an object is nil (nothing).

Ruby

object.nil? # returns true if object is nil

Sample Program

This program defines a predicate method positive? that checks if a number is greater than zero. It prints true or false based on the input.

Ruby

def positive?(number)
  number > 0
end

puts positive?(5)   # true
puts positive?(-3)  # false
puts positive?(0)   # false

Important Notes

Predicate methods should never change the object they check; they only answer yes/no questions.

Use predicate methods to make your code more readable and expressive.

Summary

Predicate methods end with a ? and return true or false.

They help check conditions clearly and simply.

Use them to ask yes/no questions about data or objects.