Instance_variable_get and set in Ruby - Step-by-Step Execution

Concept Flow - Instance_variable_get and set

Create Object

↓

Set Instance Variable

↓

Get Instance Variable

↓

Use or Display Value

↓

End

This flow shows creating an object, setting an instance variable, getting its value, and using it.

Execution Sample

Ruby

class Person
  def initialize(name)
    @name = name
  end
end

p = Person.new("Alice")
p.instance_variable_get(:@name)

Creates a Person object with a name and gets the value of the @name instance variable.

Execution Table

Step	Action	Code/Method	Instance Variable State	Output
1	Create Person object	Person.new("Alice")	@name = "Alice"	Person object created
2	Initialize @name	initialize("Alice")	@name = "Alice"	None
3	Get @name value	instance_variable_get(:@name)	@name = "Alice"	"Alice"
4	Set @age value	instance_variable_set(:@age, 30)	@name = "Alice", @age = 30	30
5	Get @age value	instance_variable_get(:@age)	@name = "Alice", @age = 30	30
6	Get non-existing @height	instance_variable_get(:@height)	@name = "Alice", @age = 30	nil
7	End	-	@name = "Alice", @age = 30	Execution ends

💡 All instance variables set or retrieved; no more actions.

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
@name	nil	"Alice"	"Alice"	"Alice"
@age	nil	nil	30	30
@height	nil	nil	nil	nil

Key Moments - 3 Insights

Why does instance_variable_get return nil for @height?

Because @height was never set on the object, instance_variable_get returns nil as shown in step 6 of the execution_table.

Can instance_variable_set create a new instance variable?

Yes, instance_variable_set creates or updates the variable. Step 4 shows @age being created and set to 30.

Does instance_variable_get require the variable name as a symbol or string?

It accepts the variable name as a symbol or string starting with @, like :@name, as used in steps 3 and 5.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output of step 3?

A nil

B 30

C "Alice"

D Error

💡 Hint

Check the Output column for step 3 in the execution_table.

At which step is the @age instance variable created and set?

A Step 4

B Step 2

C Step 5

D Step 6

💡 Hint

Look at the Instance Variable State column to see when @age appears.

If you call instance_variable_get(:@height) before setting it, what will be returned?

A An error

B nil

C "height"

D 0

💡 Hint

Refer to step 6 in the execution_table and the variable_tracker row for @height.

Concept Snapshot

Instance_variable_get(:@var) returns the value of @var or nil if unset.
Instance_variable_set(:@var, value) sets or creates @var with value.
Use symbols or strings with @ prefix for variable names.
Useful to access or change variables dynamically.
Does not call getter/setter methods, works directly on variables.

Full Transcript

This visual execution shows how Ruby's instance_variable_get and instance_variable_set methods work. First, a Person object is created with @name set to "Alice". Using instance_variable_get(:@name) returns "Alice". Then, instance_variable_set(:@age, 30) creates a new instance variable @age with value 30. Getting @age returns 30. Trying to get an unset variable like @height returns nil. These methods let you read or write instance variables dynamically by name, without using normal getter or setter methods.