Method chaining patterns in Ruby - Mini Project: Build & Apply

Method chaining patterns

📖 Scenario: Imagine you are working with a list of book titles in a library system. You want to process these titles by cleaning up the text and then selecting only the titles that meet certain conditions.

🎯 Goal: You will build a Ruby program that uses method chaining to clean and filter a list of book titles step-by-step.

📋 What You'll Learn

Create an array of book titles with exact values

Create a variable for the minimum length of titles to keep

Use method chaining to clean and filter the titles

Print the final filtered list of titles

💡 Why This Matters

🌍 Real World

Cleaning and filtering lists of text data is common in apps like library catalogs, contact lists, or product inventories.

💼 Career

Understanding method chaining helps you write clean, readable code for data processing tasks in Ruby development jobs.

1

Create the initial array of book titles

Create an array called book_titles with these exact strings: " The Hobbit ", "War and Peace", "1984", " Brave New World ", and "Ulysses".

Ruby

# Create the array book_titles with the exact titles
# Your code here

Hint

Use square brackets [] to create an array and include the exact strings with quotes.

2

Set the minimum title length

Create a variable called min_length and set it to 10.

Ruby

book_titles = ["  The Hobbit  ", "War and Peace", "1984", " Brave New World ", "Ulysses"]
# Create min_length variable and set it to 10
# Your code here

Hint

Just assign the number 10 to the variable min_length.

3

Use method chaining to clean and filter titles

Create a new variable called filtered_titles that uses method chaining on book_titles to first remove extra spaces from each title using map(&:strip), then select only titles with length greater than or equal to min_length using select.

Ruby

book_titles = ["  The Hobbit  ", "War and Peace", "1984", " Brave New World ", "Ulysses"]
min_length = 10
# Use method chaining to strip spaces and filter by min_length
# Your code here

Hint

Use map(&:strip) to remove spaces, then select with a block to keep titles with length >= min_length.

4

Print the filtered titles

Write a puts statement to print the filtered_titles array.

Ruby

book_titles = ["  The Hobbit  ", "War and Peace", "1984", " Brave New World ", "Ulysses"]
min_length = 10
filtered_titles = book_titles.map(&:strip).select { |title| title.length >= min_length }
# Print the filtered_titles array
# Your code here

Hint

Use puts filtered_titles to print each title on its own line.

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