Super keyword behavior in Ruby

Introduction

The super keyword helps you call a method from a parent class inside a child class. It lets you reuse and extend code easily.

When you want to add extra steps to a method but keep the original behavior.

When you override a method but still need the parent class's version to run.

When you build on top of existing code without rewriting it.

When you want to keep your code organized and avoid duplication.

Syntax

Ruby

super
super()
super(arg1, arg2)

super without parentheses passes all arguments from the current method to the parent method.

super() calls the parent method with no arguments, even if the current method has some.

Examples

This calls the parent greet method with the same argument, then adds a new message.

Ruby

class Parent
  def greet(name)
    puts "Hello, #{name}!"
  end
end

class Child < Parent
  def greet(name)
    super
    puts "Welcome!"
  end
end

Child.new.greet("Alice")

Here, super() calls the parent method with no arguments, even if the child method had some.

Ruby

class Parent
  def greet
    puts "Hello!"
  end
end

class Child < Parent
  def greet
    super()
    puts "Welcome!"
  end
end

Child.new.greet

This calls the parent add method with specific arguments and then doubles the result.

Ruby

class Parent
  def add(a, b)
    a + b
  end
end

class Child < Parent
  def add(a, b)
    result = super(a, b)
    result * 2
  end
end

puts Child.new.add(3, 4)

Sample Program

The Dog class calls the speak method from Animal using super, then adds its own message.

Ruby

class Animal
  def speak(sound)
    puts "Animal says: #{sound}"
  end
end

class Dog < Animal
  def speak(sound)
    super
    puts "Dog wags tail."
  end
end

Dog.new.speak("Woof")

Important Notes

If the parent method does not exist, calling super will cause an error.

Using super helps keep code DRY (Don't Repeat Yourself).

Summary

super calls the parent class's method from a child class.

Without parentheses, super passes all current arguments to the parent method.

With empty parentheses super(), it calls the parent method with no arguments.

Practice

1. What does the super keyword do in Ruby?

easy

A. Creates a new instance of the parent class

B. Overrides the parent class's method permanently

C. Calls the parent class's method with the same name

D. Deletes the parent class's method

Solution

1. Step 1: Understand the role of super

   The super keyword is used inside a child class method to call the method with the same name from its parent class. It does not create, override, or delete methods but simply calls the parent method to reuse or extend its behavior.

2. Final Answer:

   Calls the parent class's method with the same name -> Option C

3. Quick Check:

   super calls parent method [OK]

Hint: Remember: super calls parent method with same name [OK]

Common Mistakes:

• Thinking super creates or deletes methods
• Confusing super with instance creation
• Assuming super overrides methods permanently

2. Which of the following is the correct syntax to call the parent method with no arguments using super?

easy

A. super()

B. super[]

C. super

D. super{}

Solution

1. Step 1: Understand super with parentheses

   Using super() calls the parent method explicitly with no arguments, ignoring any current method arguments. Only super() uses parentheses correctly to pass no arguments; other forms are invalid syntax.

2. Final Answer:

   super() -> Option A

3. Quick Check:

   super() means no arguments [OK]

Hint: Use parentheses to call parent with no args: super() [OK]

Common Mistakes:

• Using super without parentheses to mean no arguments
• Using brackets or braces instead of parentheses
• Confusing super() with super without parentheses

3. What will be the output of this Ruby code?

class Parent
  def greet(name)
    "Hello, #{name} from Parent"
  end
end

class Child < Parent
  def greet(name)
    super + " and Child"
  end
end

puts Child.new.greet("Alice")

medium

A. Hello, Alice from Parent and Child

B. Hello, Alice from Child

C. Hello, from Parent and Child

D. Error: wrong number of arguments

Solution

1. Step 1: Trace the method call in Child#greet

   The Child's greet method calls super without parentheses, so it passes the argument "Alice" to Parent#greet. Parent#greet returns "Hello, Alice from Parent". Child appends " and Child" to this string.

2. Final Answer:

   Hello, Alice from Parent and Child -> Option A

3. Quick Check:

   super passes args, output combines strings [OK]

Hint: super without () passes all args automatically [OK]

Common Mistakes:

• Assuming super passes no arguments by default
• Expecting an error due to argument mismatch
• Ignoring the appended string in Child method

4. Identify the error in this Ruby code:

class Parent
  def initialize(age)
    @age = age
  end
end

class Child < Parent
  def initialize
    super
    @name = "Child"
  end
end

Child.new

medium

A. NameError for @name variable

B. No error, code runs fine

C. SyntaxError due to missing parentheses

D. ArgumentError: wrong number of arguments for super

Solution

1. Step 1: Check Parent initialize method

   Parent's initialize requires one argument age. Child's initialize calls super without arguments, so it tries to call Parent's initialize with zero arguments, causing an ArgumentError.

2. Final Answer:

   ArgumentError: wrong number of arguments for super -> Option D

3. Quick Check:

   super must match parent args or use super() [OK]

Hint: super without args passes current args; mismatch causes error [OK]

Common Mistakes:

• Assuming super() passes parent's required args automatically
• Ignoring that Parent requires an argument
• Thinking missing parentheses cause syntax error here

5. Given this code, what will Child.new.greet output?

class Parent
  def greet(name = "Guest")
    "Hello, #{name} from Parent"
  end
end

class Child < Parent
  def greet(name = nil)
    if name
      super(name.upcase)
    else
      super()
    end
  end
end

puts Child.new.greet
puts Child.new.greet("alice")

hard

A. Hello, from Parent
Hello, alice from Parent

B. Hello, Guest from Parent
Hello, ALICE from Parent

C. Hello, Guest from Parent
Hello, alice from Parent

D. Error due to wrong arguments in super calls

Solution

1. Step 1: Analyze Child#greet with no argument

   When called without argument, name is nil, so super() calls Parent#greet with no arguments, using default "Guest". When called with "alice", name.upcase is "ALICE" passed to super(name.upcase), so Parent#greet returns "Hello, ALICE from Parent".

2. Final Answer:

   Hello, Guest from Parent Hello, ALICE from Parent -> Option B

3. Quick Check:

   super() calls parent with defaults; super(args) passes modified args [OK]

Hint: Use super() for no args, super(args) to pass specific args [OK]

Common Mistakes:

• Assuming super() passes current args
• Ignoring default parameter in Parent#greet
• Not uppercasing the argument before passing