Method chaining patterns in Ruby - Time & Space Complexity

Time Complexity: Method chaining patterns

O(n)

Understanding Time Complexity

We want to understand how the time taken by method chaining changes as the input grows.

How does calling many methods one after another affect performance?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class NumberList
  def initialize(numbers)
    @numbers = numbers
  end

  def double
    @numbers = @numbers.map { |n| n * 2 }
    self
  end

  def select_even
    @numbers = @numbers.select(&:even?)
    self
  end

  def sum
    @numbers.reduce(0, :+)
  end
end

list = NumberList.new((1..1000).to_a)
result = list.double.select_even.sum
puts result

This code doubles numbers, selects even ones, then sums them, using method chaining.

Identify Repeating Operations

Look for loops or repeated work inside each method.

• Primary operation: Each method uses array traversal (map, select, reduce).
• How many times: Each traversal goes through all elements once per method call.

How Execution Grows With Input

Each method processes the whole list, so time grows with list size.

Input Size (n)	Approx. Operations
10	About 30 (3 passes over 10 items)
100	About 300 (3 passes over 100 items)
1000	About 3000 (3 passes over 1000 items)

Pattern observation: Operations increase roughly in direct proportion to input size.

Final Time Complexity

Time Complexity: O(n)

This means the time grows linearly with the number of items processed.

Common Mistake

[X] Wrong: "Method chaining makes the code run faster because it looks shorter."

[OK] Correct: Each method still processes the whole list separately, so chaining can add up the work, not reduce it.

Interview Connect

Understanding how method chaining affects time helps you write clear and efficient code, a skill valued in real projects and interviews.

Self-Check

"What if the methods were combined into one that does all steps in a single pass? How would the time complexity change?"

Practice

1. What is the main purpose of method chaining in Ruby?

easy

A. To call multiple methods on the same object in one line

B. To create new objects automatically

C. To run methods in parallel threads

D. To convert objects into strings

Solution

1. Step 1: Understand method chaining concept

   Method chaining allows calling several methods one after another on the same object without repeating the object name.

2. Step 2: Identify the main purpose

   The main goal is to write shorter, cleaner code by linking method calls in one line.

3. Final Answer:

   To call multiple methods on the same object in one line -> Option A

4. Quick Check:

   Method chaining = calling multiple methods on one object [OK]

Hint: Method chaining links calls on one object in one line [OK]

Common Mistakes:

• Thinking it creates new objects automatically
• Confusing with threading or parallel execution
• Believing it converts objects to strings

2. Which of the following is the correct syntax for method chaining in Ruby?

easy

A. object|method1|method2|method3

B. object.method1.method2.method3

C. object::method1::method2::method3

D. object->method1->method2->method3

Solution

1. Step 1: Recall Ruby method call syntax

   In Ruby, methods are called on objects using dot notation: object.method.

2. Step 2: Identify chaining syntax

   Method chaining uses multiple dots to call methods one after another on the same object.

3. Final Answer:

   object.method1.method2.method3 -> Option B

4. Quick Check:

   Ruby chaining uses dots between methods [OK]

Hint: Use dots (.) to chain methods in Ruby [OK]

Common Mistakes:

• Using arrows (->) which is not Ruby syntax
• Using double colons (::) which are for constants or modules
• Using pipes (|) which are not method call operators

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

class Box
  def initialize(value)
    @value = value
  end

  def add(x)
    @value += x
    self
  end

  def multiply(x)
    @value *= x
    self
  end

  def value
    @value
  end
end

box = Box.new(2)
result = box.add(3).multiply(4).value
puts result

medium

A. 20

B. 14

C. 10

D. 8

Solution

1. Step 1: Trace the add method

   Start with @value = 2. add(3) adds 3: 2 + 3 = 5, returns self.

2. Step 2: Trace the multiply method

   multiply(4) multiplies @value by 4: 5 * 4 = 20, returns self.

3. Step 3: Call value method

   value returns @value which is 20.

4. Final Answer:

   20 -> Option A

5. Quick Check:

   2 + 3 = 5; 5 * 4 = 20 [OK]

Hint: Follow each method step-by-step, remember self returns object [OK]

Common Mistakes:

• Forgetting that add and multiply return self
• Calculating operations in wrong order
• Returning intermediate values instead of final

4. Identify the error in the following Ruby code that tries to chain methods:

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

  def greet
    puts "Hello, #{@name}!"
  end

  def farewell
    puts "Goodbye, #{@name}!"
  end
end

p = Person.new("Sam")
p.greet.farewell

medium

A. initialize method missing return statement

B. farewell method is misspelled

C. Cannot create Person object with new

D. greet method does not return self, so chaining fails

Solution

1. Step 1: Check method return values

   greet prints a message but returns nil (default for puts).

2. Step 2: Understand chaining requirement

   For chaining, greet must return self to allow calling farewell next.

3. Final Answer:

   greet method does not return self, so chaining fails -> Option D

4. Quick Check:

   Method chaining needs methods to return self [OK]

Hint: Ensure methods return self to chain calls [OK]

Common Mistakes:

• Assuming puts returns self
• Thinking initialize needs explicit return
• Believing object creation is the problem

5. You want to create a Ruby class TextFormatter that allows chaining methods to transform a string. The methods are:
- upcase: converts text to uppercase
- reverse: reverses the text
- append(str): adds str to the end

Which implementation correctly supports chaining all these methods and returns the final string with result?

hard

A. Each method prints the modified string and returns nil

B. Each method returns the modified string directly without returning self

C. Each method modifies @text, returns self; add a result method returning @text

D. Each method returns a new TextFormatter object with modified text

Solution

1. Step 1: Understand chaining requirements

   To chain methods, each must return self (the object) so next method can be called.

2. Step 2: Provide final output method

   Since methods return self, a separate method (like result) should return the final string.

3. Final Answer:

   Each method modifies @text, returns self; add a result method returning @text -> Option C

4. Quick Check:

   Return self to chain, separate method to get final string [OK]

Hint: Return self in methods, separate method returns final value [OK]

Common Mistakes:

• Returning strings breaks chaining
• Printing inside methods returns nil
• Returning new objects breaks original chain