Instance variables (@) in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an instance variable in Ruby?

An instance variable in Ruby is a variable that belongs to a specific object (instance) of a class. It starts with the @ symbol and stores data unique to that object.

beginner

How do you declare an instance variable inside a Ruby class?

You declare an instance variable by prefixing the variable name with @ inside any method of the class, usually inside the initialize method.

beginner

Why do instance variables start with @ in Ruby?

The @ symbol tells Ruby that the variable is tied to a specific object instance, not a local or global variable. It helps Ruby keep track of data for each object separately.

intermediate

Can instance variables be accessed directly outside the class?

No, instance variables are private to the object. To access them outside the class, you need to use methods like getters or attr_reader.

beginner

Example: What does this code print?
<pre>class Dog
  def initialize(name)
    @name = name
  end
  def speak
    "Woof! My name is #{@name}"
  end
end

dog = Dog.new("Buddy")
puts dog.speak</pre>

It prints: Woof! My name is Buddy The @name instance variable stores the dog's name and is used inside the speak method.

What symbol is used to start an instance variable in Ruby?

A @

B $

C #

D &

Instance variables in Ruby always start with the @ symbol.

Where are instance variables typically declared in a Ruby class?

A Outside the class

B Inside the initialize method

C Inside a global method

D In a local variable

Instance variables are usually set inside the initialize method to store object-specific data.

Can you access an instance variable directly from outside the object?

A No, you need a method to access it

B Yes, always

C Only if it starts with $

D Only inside a module

Instance variables are private to the object; you must use methods like getters to access them.

What does @name represent inside a Ruby class?

A A constant

B A local variable

C A global variable

D An instance variable

The @ symbol means the variable is an instance variable tied to the object.

If you create two objects from the same class, do they share the same instance variables?

A Only if they are global

B Yes, instance variables are shared

C No, each object has its own instance variables

D Only if declared outside methods

Each object has its own copy of instance variables, so data is unique per object.

Explain what an instance variable is in Ruby and why it starts with @.

Think about how Ruby keeps data unique for each object.

Describe how you would use instance variables to store and access a person's name in a Ruby class.

Consider how to keep the name inside the object and show it outside.