Predicate methods (ending with ?) in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a predicate method in Ruby?

A predicate method is a method that ends with a question mark (?) and returns a boolean value (true or false). It answers a yes/no question about an object.

beginner

Why do predicate methods in Ruby end with a question mark (?)?

The question mark at the end signals that the method returns a boolean value, making it clear the method answers a yes/no question.

beginner

Example: What does the Ruby method `empty?` do when called on an array?

The `empty?` method returns true if the array has no elements, otherwise it returns false.

intermediate

How would you define a custom predicate method in Ruby?

Define a method ending with `?` that returns true or false based on a condition. For example:<br>

def adult?(age)
  age >= 18
end

intermediate

Can predicate methods return values other than true or false?

Technically yes, but by convention predicate methods should return only true or false to clearly indicate a yes/no answer.

What does a predicate method in Ruby always return?

A true or false

B a string

C an integer

D nil

Predicate methods always return true or false to answer yes/no questions.

Which of these is a valid predicate method name in Ruby?

A valid?

B check

C run!

D start

Predicate methods end with a question mark (?), like 'valid?'.

What does the Ruby method `nil?` check?

A If an object is empty

B If an object is a number

C If an object is true

D If an object is nil

`nil?` returns true if the object is nil, otherwise false.

How do you call a predicate method named `empty?` on an array named `arr`?

A arr.empty

B empty?(arr)

C arr.empty?

D empty.arr?

Predicate methods are called like any other method: object.method_name?.

Why is it helpful to use predicate methods?

A They speed up the program

B They make code easier to read by clearly showing yes/no checks

C They return strings

D They create new objects

Predicate methods improve readability by signaling boolean checks.

Explain what a predicate method is and why it ends with a question mark in Ruby.

Think about how Ruby shows methods that answer true or false questions.

Write a simple custom predicate method in Ruby that checks if a number is even.

Use the modulo operator (%) to check even numbers.