Why YARD for documentation in Ruby? - Purpose & Use Cases

The Big Idea

Discover how a simple tool can turn messy notes into clear, helpful guides that save hours of confusion!

The Scenario

Imagine you wrote a Ruby program with many methods and classes. Now, you want to explain how each part works to your team or your future self. You try writing notes in plain text files or comments scattered everywhere.

Later, when you or someone else reads the code, it's hard to find clear explanations or understand how to use each method quickly.

The Problem

Writing documentation manually in separate files or messy comments is slow and confusing. It's easy to forget to update notes when code changes. This leads to outdated or missing information, causing frustration and mistakes.

Also, searching through long comments or external files wastes time and breaks your focus.

The Solution

YARD is a tool that helps you write clear, structured documentation right inside your Ruby code using special comment tags. It automatically generates neat, easy-to-read HTML pages from these comments.

This keeps your docs close to the code, always up to date, and easy to browse. It saves time and helps everyone understand your code better.

Before vs After

✗ Before

# This method adds two numbers
# but you have to read code to understand it
def add(a, b)
  a + b
end

✓ After

# Adds two numbers and returns the sum.
# @param a [Integer] the first number
# @param b [Integer] the second number
# @return [Integer] the sum of a and b
def add(a, b)
  a + b
end

What It Enables

YARD makes it easy to create professional, searchable documentation that helps you and others use and maintain Ruby code confidently.

Real Life Example

When working on a team project, YARD lets everyone quickly find how to use shared methods without guessing or asking, speeding up development and reducing bugs.

Key Takeaways

Manual documentation is slow and often outdated.

YARD integrates docs inside Ruby code with special comments.

It generates clear, easy-to-navigate HTML documentation automatically.

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