Instance variables (@) in Ruby - Step-by-Step Execution

Concept Flow - Instance variables (@)

Create Object

↓

Initialize Instance Variables

↓

Use Instance Variables in Methods

↓

Access or Modify Instance Variables

↓

Object Maintains Its Own Data

When an object is created, instance variables start with @ and store data unique to that object. Methods can read or change these variables.

Execution Sample

Ruby

class Person
  def initialize(name)
    @name = name
  end
  def greet
    "Hello, #{@name}!"
  end
end
p = Person.new("Anna")
p.greet

Creates a Person object with a name stored in @name, then greets using that name.

Execution Table

Step	Action	Instance Variable @name	Output
1	Create Person object with name 'Anna'	nil -> 'Anna'
2	Call greet method	'Anna'	"Hello, Anna!"
3	End of program	'Anna'

💡 Program ends after greet method returns the greeting string.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
@name	nil	'Anna'	'Anna'	'Anna'

Key Moments - 2 Insights

Why do we use @ before the variable name?

The @ sign marks the variable as an instance variable, meaning it belongs to the object and keeps its value between method calls, as shown in step 1 and 2 of the execution_table.

Can instance variables be accessed outside the object directly?

No, instance variables are private to the object. You access them through methods like greet(), as seen in step 2 where @name is used inside the method.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of @name after creating the Person object?

A "Hello, Anna!"

B nil

C 'Anna'

D undefined

💡 Hint

Check Step 1 in execution_table where @name changes from nil to 'Anna'.

At which step does the greet method use the instance variable @name?

A Step 1

B Step 2

C Step 3

D None

💡 Hint

Look at Step 2 in execution_table where greet method is called and @name is used.

If we create another Person object with name 'Bob', what will @name be for that object?

A 'Bob'

B 'Anna'

C nil

D shared between objects

💡 Hint

Instance variables are unique to each object, as shown by @name holding 'Anna' for the first object.

Concept Snapshot

Instance variables start with @ and belong to an object.
They store data unique to that object.
Set them in initialize or other methods.
Access them inside methods with @name.
Each object has its own copy.
They are private to the object.

Full Transcript

In Ruby, instance variables start with @ and belong to each object created from a class. When you create an object, you can set instance variables to store data unique to that object. For example, in the Person class, @name stores the person's name. Methods inside the class can use these variables to work with the object's data. Instance variables keep their values as long as the object exists. They cannot be accessed directly from outside the object but only through methods. This helps keep data safe and organized per object.