Method_added hook in Ruby - Step-by-Step Execution

Concept Flow - Method_added hook

Define class

↓

Define method

↓

Ruby detects new method

↓

Trigger method_added hook

↓

Execute method_added code

↓

Continue defining class/methods or finish

When a new method is defined in a Ruby class or module, Ruby automatically calls the method_added hook if it is defined, allowing custom code to run right after method creation.

Execution Sample

Ruby

class MyClass
  def self.method_added(name)
    puts "Added method: #{name}"
  end

  def greet
    puts 'Hello'
  end
end

This code shows how Ruby calls method_added hook after defining the greet method, printing the method name.

Execution Table

Step	Action	Method Name Detected	Hook Called	Output
1	Start class definition	-	No	-
2	Define method_added hook	-	No	-
3	Define method greet	greet	Yes	Added method: greet
4	Class definition ends	-	No	-

💡 Class definition ends, no more methods added, hook no longer triggered

Variable Tracker

Variable	Start	After Step 3	Final
name	-	:greet	:greet

Key Moments - 3 Insights

Why does method_added receive the method name as a symbol?

Because Ruby passes the newly defined method's name as a symbol to method_added, as shown in execution_table step 3 where 'greet' is passed as :greet.

Does method_added get called when defining the hook itself?

No, method_added is not called when defining itself, only when other methods are added, as seen in execution_table steps 1 and 2.

Can method_added be used to track all methods added to a class?

Yes, method_added runs every time a new method is defined, so it can track all methods, demonstrated by the hook printing method names in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output when the greet method is defined?

A method_added hook called

B Added method: greet

C Hello

D No output

💡 Hint

Check the Output column at Step 3 in the execution_table.

At which step does Ruby call the method_added hook?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the Hook Called column in the execution_table.

If you add another method after greet, what will happen?

A method_added hook will not run

B The class will crash

C method_added hook will run again with new method name

D The greet method will be removed

💡 Hint

method_added runs every time a new method is defined, as shown in the concept_flow.

Concept Snapshot

method_added is a Ruby hook method called automatically when a new method is defined in a class or module.
It receives the new method's name as a symbol.
Use it to run custom code right after method creation.
It does not trigger when defining itself.
Useful for tracking or modifying methods dynamically.

Full Transcript

In Ruby, when you define a new method inside a class or module, Ruby automatically calls a special hook method called method_added if it exists. This hook receives the name of the new method as a symbol. For example, if you define a method named greet, Ruby calls method_added(:greet). This lets you run code right after a method is created, such as printing the method name. The method_added hook itself is not called when you define it, only for other methods added later. This feature is useful to track or modify methods dynamically as they are defined.