Class methods with self prefix in Ruby - Step-by-Step Execution

Concept Flow - Class methods with self prefix

Define class

↓

Define method with self.

↓

Call method on class

↓

Execute method body

↓

Return result

↓

Output result

This flow shows how a class method defined with self. is called on the class itself and executes its code.

Execution Sample

Ruby

class Greeting
  def self.say_hello
    "Hello from class method!"
  end
end

puts Greeting.say_hello

Defines a class method say_hello and calls it on the Greeting class to print a message.

Execution Table

Step	Action	Evaluation	Result
1	Define class Greeting	Class Greeting created	Class Greeting ready
2	Define method self.say_hello	Method say_hello added to Greeting class	Method ready
3	Call Greeting.say_hello	Invoke class method	Method body runs
4	Execute method body	Return string "Hello from class method!"	"Hello from class method!"
5	puts output	Print string to console	Hello from class method!

💡 Method returns string and program ends after printing output

Variable Tracker

Variable	Start	After call	Final
Greeting	Class defined	Class exists	Class exists
say_hello (method)	Not defined	Defined on Greeting	Defined on Greeting
Return value	None	None	"Hello from class method!"

Key Moments - 2 Insights

Why do we use self. before method name?

Using self. defines the method as a class method, so it belongs to the class itself, not instances. See execution_table step 2 where method is added to class.

Can we call say_hello without self. prefix?

No, without self. it becomes an instance method. Here, we call Greeting.say_hello on the class, so method must be defined with self. (see step 3).

Visual Quiz - 3 Questions

Look at the execution table, what is the result returned by the class method at step 4?

A nil

B An error

C "Hello from class method!"

D "say_hello"

💡 Hint

Check the 'Result' column at step 4 in execution_table

At which step is the method say_hello defined as a class method?

A Step 2

B Step 3

C Step 1

D Step 5

💡 Hint

Look at the 'Action' column for method definition in execution_table

If we remove self. from method definition, what will happen when calling Greeting.say_hello?

A It will print the message as before

B It will raise a NoMethodError

C It will call an instance method automatically

D It will return nil

💡 Hint

Recall key_moments about method type and how class methods are called

Concept Snapshot

Class methods use self. prefix in method definition.
Called on the class itself, not instances.
Syntax: def self.method_name
Use for behavior related to the class as a whole.
Called like ClassName.method_name.
Without self., methods are instance methods.

Full Transcript

This example shows how to define and call a class method in Ruby using the self. prefix. The class Greeting is defined, then a method say_hello is defined with self. to make it a class method. When we call Greeting.say_hello, Ruby runs the method body and returns the string "Hello from class method!" which is printed. The execution table traces each step: defining the class, defining the method, calling the method, returning the string, and printing it. The variable tracker shows the class and method states. Key moments clarify why self. is needed and what happens if it is removed. The quiz tests understanding of the method return value, definition step, and behavior without self. The snapshot summarizes the key points about class methods with self. prefix.