YARD for documentation in Ruby - Mini Project: Build & Apply

Documenting Ruby Code with YARD

📖 Scenario: You are working on a small Ruby project that calculates areas of different shapes. To help your team understand your code better, you want to add clear documentation using YARD, a popular Ruby documentation tool.

🎯 Goal: Learn how to write YARD documentation comments for Ruby methods and classes, so your code is easy to understand and maintain.

📋 What You'll Learn

Create a Ruby class with methods

Add YARD documentation comments to the class and methods

Use tags like @param and @return in the comments

Print the result of method calls to verify functionality

💡 Why This Matters

🌍 Real World

Clear documentation helps teams understand code quickly and reduces bugs when working on projects together.

💼 Career

Many Ruby jobs require writing and maintaining well-documented code using tools like YARD to improve code quality and collaboration.

1

Create a Ruby class with methods

Create a Ruby class called ShapeCalculator with two methods: area_of_square that takes side as a parameter and returns the area of the square, and area_of_circle that takes radius as a parameter and returns the area of the circle (use 3.14 for π).

Ruby

# Create the ShapeCalculator class with two methods
class ShapeCalculator
  # Your code here
end

Hint

Define a class with class ShapeCalculator and add two methods with def. Use simple math to calculate areas.

2

Add YARD documentation comments to the class

Add a YARD documentation comment above the ShapeCalculator class that briefly describes the class purpose using # comments.

Ruby

# Add a YARD comment describing the ShapeCalculator class
# Your code here
class ShapeCalculator
  def area_of_square(side)
    side * side
  end

  def area_of_circle(radius)
    3.14 * radius * radius
  end
end

Hint

Use # to write a short description above the class definition.

3

Add YARD documentation comments to methods

Add YARD documentation comments above both methods. For area_of_square, add @param side [Numeric] and @return [Numeric] tags. For area_of_circle, add @param radius [Numeric] and @return [Numeric] tags. Also add a short description for each method.

Ruby

# Add YARD comments for both methods
# Your code here
# Calculates areas of different shapes
class ShapeCalculator
  def area_of_square(side)
    side * side
  end

  def area_of_circle(radius)
    3.14 * radius * radius
  end
end

Hint

Use # comments with @param and @return tags above each method.

4

Print results of method calls

Create an instance of ShapeCalculator called calculator. Then print the result of calculator.area_of_square(4) and calculator.area_of_circle(3).

Ruby

# Create an instance and print the results
# Your code here
# Calculates areas of different shapes
class ShapeCalculator
  # Calculates the area of a square
  # @param side [Numeric] the length of one side of the square
  # @return [Numeric] the area of the square
  def area_of_square(side)
    side * side
  end

  # Calculates the area of a circle
  # @param radius [Numeric] the radius of the circle
  # @return [Numeric] the area of the circle
  def area_of_circle(radius)
    3.14 * radius * radius
  end
end

Hint

Create an object with ShapeCalculator.new and use puts to print method results.

Practice

1. What is the main purpose of using YARD in Ruby code?

easy

A. To automatically fix syntax errors in Ruby code

B. To speed up the execution of Ruby programs

C. To write clear documentation inside the code using special comments

D. To convert Ruby code into other programming languages

Solution

1. Step 1: Understand YARD's role

   YARD is a tool to add documentation inside Ruby code using comments.

2. Step 2: Identify the correct purpose

   It helps explain code clearly, not speed execution or fix errors.

3. Final Answer:

   To write clear documentation inside the code using special comments -> Option C

4. Quick Check:

   YARD -> documentation [OK]

Hint: YARD is for documentation, not code execution [OK]

Common Mistakes:

• Thinking YARD runs or speeds up code
• Confusing YARD with debugging tools
• Assuming YARD converts code to other languages

2. Which of the following is the correct way to document a method parameter using YARD?

easy

A. # @param name [String] the user's name

B. // @param name String the user's name

C. /* @param name String the user's name */

D.

Solution

1. Step 1: Recognize Ruby comment style

   Ruby uses # for single-line comments, so YARD tags must start with #.

2. Step 2: Identify correct YARD tag syntax

   The correct format is "# @param name [Type] description".

3. Final Answer:

   # @param name [String] the user's name -> Option A

4. Quick Check:

   # -> Ruby comments [OK]

Hint: YARD tags start with # in Ruby code comments [OK]

Common Mistakes:

• Using comment styles from other languages
• Omitting square brackets around type
• Writing tags inside HTML or block comments

3. What will be the output of the following YARD comment when generating documentation?

# Adds two numbers
# @param a [Integer] first number
# @param b [Integer] second number
# @return [Integer] sum of a and b
# @example
#   add(2, 3) #=> 5
def add(a, b)
  a + b
end

medium

A. Only the method name will appear without any details

B. Syntax error because @example is not allowed

C. The code will run and print 5

D. Documentation showing method description, parameters with types, return type, and example usage

Solution

1. Step 1: Understand YARD comment tags

   The tags @param, @return, and @example describe method details for documentation.

2. Step 2: Recognize YARD output

   YARD generates HTML docs showing description, parameters, return type, and examples.

3. Final Answer:

   Documentation showing method description, parameters with types, return type, and example usage -> Option D

4. Quick Check:

   YARD tags -> detailed docs [OK]

Hint: YARD tags create detailed docs, not runtime output [OK]

Common Mistakes:

• Confusing documentation comments with code execution
• Thinking @example causes errors
• Expecting code output instead of docs

4. Identify the error in this YARD comment block:

# @param name String the user's name
# @return String greeting message
def greet(name)
  "Hello, #{name}!"
end

medium

A. Missing square brackets around the type in @param and @return tags

B. The method name should be capitalized

C. YARD comments must be placed after the method definition

D. The string interpolation syntax is incorrect

Solution

1. Step 1: Check YARD tag syntax

   YARD requires types in square brackets, e.g., [String], not just String.

2. Step 2: Verify other parts

   Method name capitalization and comment placement are correct; string interpolation is valid Ruby.

3. Final Answer:

   Missing square brackets around the type in @param and @return tags -> Option A

4. Quick Check:

   [Type] -> YARD requirement [OK]

Hint: Always put types in square brackets in YARD tags [OK]

Common Mistakes:

• Omitting square brackets around types
• Placing comments after method instead of before
• Confusing Ruby syntax errors with documentation errors

5. You want to document a Ruby class with YARD that has a method returning a hash with keys as symbols and values as arrays of strings. Which is the best way to write the @return tag for this method?

hard

A. # @return [Hash] a hash with keys and values

B. # @return [Hash{Symbol => Array<String>}] a hash mapping symbols to arrays of strings

C. # @return [Array<Hash>] an array of hashes

D. # @return [Hash(Symbol, Array)] a hash with symbol keys and array values

Solution

1. Step 1: Understand complex type syntax in YARD

   YARD supports detailed type annotations like Hash{KeyType => ValueType}.

2. Step 2: Match the method return type

   The method returns a hash with Symbol keys and Array of String values, so use Hash{Symbol => Array<String>}.

3. Final Answer:

   # @return [Hash{Symbol => Array<String>}] a hash mapping symbols to arrays of strings -> Option B

4. Quick Check:

   Hash{Key => Value} -> correct syntax [OK]

Hint: Use Hash{KeyType => ValueType} for detailed return types [OK]

Common Mistakes:

• Using vague types like just Hash
• Incorrect syntax like Hash(Symbol, Array)
• Confusing array of hashes with hash of arrays