Super keyword behavior in Ruby - Time & Space Complexity

Time Complexity: Super keyword behavior

O(n)

Understanding Time Complexity

We want to understand how using the super keyword affects the time it takes for a program to run.

Specifically, how does calling a method from a parent class impact execution as input grows?

Scenario Under Consideration

Analyze the time complexity of the following Ruby code using super.

class Parent
  def process(items)
    items.map { |item| item * 2 }
  end
end

class Child < Parent
  def process(items)
    result = super
    result.select { |x| x > 10 }
  end
end

child = Child.new
child.process([1, 5, 10, 20])

This code doubles each item in a list using the parent method, then filters the doubled items in the child method.

Identify Repeating Operations

Look for loops or repeated actions in the code.

• Primary operation: Two loops over the list: one in the parent process method (map), and one in the child method (select).
• How many times: Each loop runs once over all items, so twice over the input list.

How Execution Grows With Input

Each item in the input list is processed twice, once for doubling and once for filtering.

Input Size (n)	Approx. Operations
10	About 20 operations (2 loops x 10 items)
100	About 200 operations
1000	About 2000 operations

Pattern observation: The total work grows roughly twice as fast as the input size.

Final Time Complexity

Time Complexity: O(n)

This means the time to run grows directly in proportion to the number of items.

Common Mistake

[X] Wrong: "Using super makes the method twice as slow in a way that changes the overall time complexity."

[OK] Correct: Calling super just adds another loop over the data, so it still grows linearly with input size, not exponentially or worse.

Interview Connect

Understanding how method calls like super affect performance helps you explain your code clearly and reason about efficiency in real projects.

Self-Check

What if the parent method used nested loops instead of a single loop? How would the time complexity change?

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