Method chaining patterns in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is method chaining in Ruby?

Method chaining is a technique where multiple methods are called in a single line, one after another, because each method returns an object that the next method can use.

beginner

Why do methods need to return self or an object for chaining to work?

For chaining, each method must return an object (often self) so the next method can be called on that returned object, allowing the chain to continue.

beginner

Example: What does this Ruby code do?

"hello".upcase.reverse

It converts "hello" to uppercase "HELLO" with upcase, then reverses it to "OLLEH" with reverse, chaining two methods in one line.

intermediate

How can method chaining improve code readability?

Method chaining lets you write clear, concise code by linking related operations in one line, making the flow easier to follow like a step-by-step recipe.

intermediate

What is a common pattern to enable method chaining in your own Ruby classes?

Define methods that perform actions and return self at the end, so you can chain multiple method calls on the same object.

In Ruby, what must a method return to allow chaining?

A An object (often self)

B nil

C A string only

D An integer

For chaining, each method must return an object so the next method can be called on it.

What will this Ruby code output?

"ruby".capitalize.reverse

A "Ybur"

B "ybuR"

C "Ruby"

D "ybur"

capitalize makes "Ruby", then reverse flips it to "ybuR" (case sensitive).

Which of these is a benefit of method chaining?

A More lines of code

B Less flexible code

C Slower execution

D Improved readability

Method chaining improves readability by linking related operations clearly.

How do you enable method chaining in your own Ruby class methods?

A Return a new object every time

B Return nil

C Return self at the end of methods

D Use global variables

Returning self allows the next method to be called on the same object.

What does this chained call do?

[1, 2, 3].map(&:to_s).join(",")

A Converts numbers to strings and joins them with commas

B Adds numbers together

C Sorts the array

D Removes duplicates

map(&:to_s) converts each number to a string, then join(",") combines them with commas.

Explain how method chaining works in Ruby and why returning self is important.

Think about how one method's output becomes the next method's input.

Describe a simple example of method chaining with strings in Ruby and what the output would be.

Use a string and two methods that change it step by step.

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