Method chaining patterns in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained string methods

What is the output of this Ruby code using method chaining?

Ruby

result = "  hello world  ".strip.upcase.reverse
puts result

A "DLROW OLLEH"

B "dlrow olleh"

C "HELLO WORLD"

D " HELLO WORLD "

💡 Hint

Think about what each method does in order: strip, upcase, then reverse.

The strip method removes spaces at the start and end, upcase converts all letters to uppercase, and reverse reverses the string. So the final output is the reversed uppercase string without spaces.

❓ Predict Output

intermediate

Chained array transformations output

What does this Ruby code print?

Ruby

numbers = [1, 2, 3, 4, 5]
result = numbers.select(&:odd?).map { |n| n * 10 }.join(",")
puts result

A "2,4"

B "1,3,5"

C "10,30,50"

D "20,40"

💡 Hint

First select odd numbers, then multiply each by 10, then join with commas.

select(&:odd?) picks odd numbers [1,3,5]. map { |n| n * 10 } multiplies each by 10 giving [10,30,50]. join(",") makes a string "10,30,50".

🔧 Debug

advanced

Identify the error in method chaining

What error does this Ruby code raise?

Ruby

result = "123abc".to_i.to_s.reverse
puts result

A NoMethodError: undefined method `reverse' for Integer

B No error, outputs "321"

C TypeError: can't convert String into Integer

D ArgumentError: invalid value for Integer()

💡 Hint

Check the return types of each method in the chain.

to_i converts string to integer 123, to_s converts back to string "123", then reverse reverses it to "321". No error occurs.

🔧 Debug

advanced

Which option raises a NoMethodError in method chaining?

Which of these Ruby code snippets will raise a NoMethodError?

A "HELLO".upcase!.reverse

B "hello".upcase.reverse

C "test".split.map(&:upcase)

D "example".reverse.upcase

💡 Hint

Bang methods like upcase! return nil if the string is not modified.

Option A: "HELLO".upcase! returns nil because the string is already uppercase (no mutation). Then nil.reverse raises NoMethodError. Options B, C, and D execute without error.

🚀 Application

expert

Count words with method chaining

Using method chaining, which code correctly counts how many words in the string have length greater than 3?

Ruby

text = "Ruby is fun and powerful"

A

count = text.split.filter { |w| w.length > 3 }.size
puts count

B

count = text.split.map { |w| w.length > 3 }.count
puts count

C

count = text.split.reduce(0) { |acc, w| acc + (w.length > 3 ? 1 : 0) }
puts count

D

count = text.split.select { |w| w.length > 3 }.count
puts count

💡 Hint

Select words longer than 3 characters, then count them.

Option D uses select to filter words with length > 3 ("Ruby", "powerful"), then count returns 2. Option D raises NoMethodError (filter undefined in standard Ruby). Option D maps to booleans and count (no arg) returns array size 5. Option D works (2) but is less idiomatic than enumerator methods.

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