Everything is an object mental model in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the 'Everything is an object' mental model mean in Ruby?

In Ruby, everything you work with is an object. Numbers, strings, methods, and even classes themselves are objects. This means they all have methods and properties you can use.

beginner

How can you call a method on a number in Ruby?

Since numbers are objects, you can call methods on them like this: 5.next which returns 6.

intermediate

Are classes in Ruby objects too?

Yes! Classes in Ruby are objects of the class Class. This means you can call methods on classes themselves.

beginner

What is the class of a string like "hello" in Ruby?

The class of "hello" is String. You can check this by calling <code>"hello".class</code> which returns <code>String</code>.

intermediate

Why is the 'Everything is an object' model helpful?

It helps you understand that you can use methods on any value, making Ruby very consistent and flexible. It also means you can extend or change behavior by adding methods to objects.

In Ruby, what is the class of the number 10?

A Integer

B Number

C Fixnum

D Object

In modern Ruby, 10 is an Integer object. Fixnum was used in older versions but now Integer covers all whole numbers.

Which of these is NOT true about Ruby's 'Everything is an object' model?

A Classes themselves are objects.

B Only strings and arrays are objects.

C You can call methods on numbers.

D Even true and false are objects.

In Ruby, everything is an object, not just strings and arrays.

What will "hello".class return in Ruby?

A Class

B Object

C Text

D String

The class of a string literal is String.

Which class do all Ruby classes belong to?

A Class

B Object

C Module

D String

All classes in Ruby are instances of the Class class.

What does calling 5.next return in Ruby?

A 7

B 5

C 6

D Error

Since 5 is an object, calling the next method returns the next integer, 6.

Explain the 'Everything is an object' mental model in Ruby and give two examples.

Think about how you can call methods on numbers and strings.

Why does Ruby treat classes as objects? How does this affect how you use classes?

Consider how classes themselves can have methods.