Creating a gem basics in Ruby - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this gemspec version code?

Consider this snippet from a gemspec file defining the gem version. What will be printed when running this Ruby code?

Ruby

module MyGem
  VERSION = "1.2.3"
end

puts MyGem::VERSION

A Error: uninitialized constant MyGem

B MyGem::VERSION

C version 1.2.3

D 1.2.3

💡 Hint

Look at how constants are accessed inside modules in Ruby.

The constant VERSION inside the module MyGem is accessed with MyGem::VERSION, which returns the string "1.2.3". The puts prints this string.

🧠 Conceptual

intermediate

Which file is essential to define a Ruby gem's metadata?

When creating a Ruby gem, which file must you create to specify the gem's name, version, summary, and authors?

A Gemfile

B gemspec

C README.md

D Rakefile

💡 Hint

This file ends with .gemspec and is used by RubyGems.

The gemspec file contains metadata about the gem such as its name, version, authors, and summary. Gemfile is for dependencies, Rakefile for tasks, README.md for documentation.

🔧 Debug

advanced

Why does this gemspec raise an error?

Look at this gemspec snippet. Why does it raise a SyntaxError? s.name = "my_gem" s.version = 0.1.0 s.summary = "A sample gem"

Ruby

Gem::Specification.new do |s|
  s.name = "my_gem"
  s.version = 0.1.0
  s.summary = "A sample gem"
end

A Version must be a string, not a float or number

B Missing comma between version numbers

C The block variable s is not defined

D The gemspec must use single quotes for strings

💡 Hint

Look carefully at the version assignment syntax.

The version must be a string like "0.1.0". Writing 0.1.0 without quotes is invalid Ruby syntax and causes a SyntaxError.

📝 Syntax

advanced

Which option correctly defines a gem's authors array in gemspec?

Select the correct syntax to assign multiple authors in a gemspec file.

Ruby

Gem::Specification.new do |s|
  s.authors = ???
end

A ["Alice", "Bob"]

B "Alice, Bob"

C {Alice, Bob}

D ("Alice", "Bob")

💡 Hint

Authors should be an array of strings.

The authors attribute expects an array of strings. Option A uses square brackets to create an array. Option A is a single string, C and D are invalid Ruby syntax for arrays.

🚀 Application

expert

How many files are created by default when running `bundle gem my_gem`?

When you run the command `bundle gem my_gem` to create a new gem skeleton, how many files are created by default (excluding hidden files)?

A 10

B 5

C 8

D 12

💡 Hint

Count files like gemspec, README, lib files, and test files generated.

By default, `bundle gem` creates around 8 files including the gemspec, README.md, Rakefile, lib directory with main file, and test files.

Practice

1. What is the main purpose of a Ruby gem?

easy

A. To compile Ruby code into machine language

B. To package and share reusable Ruby code

C. To create graphical user interfaces

D. To manage Ruby versions on your system

Solution

1. Step 1: Understand what a gem is

   A gem is a package that contains Ruby code that can be reused in different projects.

2. Step 2: Identify the main purpose

   The main purpose is to share and reuse code easily across Ruby projects.

3. Final Answer:

   To package and share reusable Ruby code -> Option B

4. Quick Check:

   Gem = reusable Ruby package [OK]

Hint: Gems are for sharing code, not compiling or GUIs [OK]

Common Mistakes:

• Thinking gems compile Ruby code
• Confusing gems with Ruby version managers
• Assuming gems create user interfaces

2. Which file is essential to define a Ruby gem's metadata and dependencies?

easy

A. README.md

B. Gemfile

C. Rakefile

D. gemspec

Solution

1. Step 1: Identify gem metadata file

   The gemspec file (.gemspec) defines the gem's name, version, authors, and dependencies.

2. Step 2: Differentiate from other files

   Gemfile manages project dependencies, Rakefile defines tasks, README.md is documentation.

3. Final Answer:

   gemspec -> Option D

4. Quick Check:

   Metadata and dependencies = gemspec [OK]

Hint: gemspec holds gem info; Gemfile is for app dependencies [OK]

Common Mistakes:

• Confusing Gemfile with gemspec
• Thinking README.md defines dependencies
• Assuming Rakefile holds gem metadata

3. Given this gemspec snippet, what is the gem's version?

Gem::Specification.new do |spec|
  spec.name        = "my_gem"
  spec.version     = "0.2.5"
  spec.summary     = "A sample gem"
end

medium

A. "0.2.5"

B. "2.5"

C. "0.2.0"

D. "1.0.0"

Solution

1. Step 1: Locate the version assignment

   The line spec.version = "0.2.5" sets the gem's version.

2. Step 2: Confirm the exact version string

   The version is exactly "0.2.5" as given in the code.

3. Final Answer:

   "0.2.5" -> Option A

4. Quick Check:

   Version in gemspec = "0.2.5" [OK]

Hint: Look for spec.version assignment in gemspec [OK]

Common Mistakes:

• Picking partial version like "0.2.0"
• Confusing version with gem name
• Assuming default version "1.0.0"

4. This gemspec file has an error. What is it?

Gem::Specification.new do |spec|
  spec.name = "example_gem"
  spec.version = 1.0.0
  spec.summary = "Example gem"
end

medium

A. Version should be a string, not a number

B. Missing spec.authors field

C. spec.name cannot have underscores

D. spec.summary must be longer than 20 characters

Solution

1. Step 1: Check version format

   The version is written as 1.0.0 without quotes, which Ruby treats as a numeric expression causing error.

2. Step 2: Correct version format

   Version must be a string like "1.0.0" with quotes to be valid.

3. Final Answer:

   Version should be a string, not a number -> Option A

4. Quick Check:

   Version must be string in gemspec [OK]

Hint: Always quote version strings in gemspec [OK]

Common Mistakes:

• Leaving version unquoted
• Thinking underscores are invalid in gem names
• Assuming summary length is strictly enforced

5. You want to create a gem that provides a method greet returning "Hello!". Which file structure and code snippet is correct? Options: A)

my_gem/
  lib/
    my_gem.rb
  my_gem.gemspec

# lib/my_gem.rb
module MyGem
  def self.greet
    "Hello!"
  end
end

B)

my_gem/
  src/
    greet.rb
  gemspec.rb

# src/greet.rb
class Greet
  def greet
    puts "Hello!"
  end
end

C)

my_gem/
  lib/
    greet.rb
  my_gem.gemspec

# lib/greet.rb
module Greet
  def greet
    "Hello!"
  end
end

D)

my_gem/
  lib/
    my_gem.rb
  my_gem.gemspec

# lib/my_gem.rb
def greet
  "Hello!"
end

hard

A. Wrong file name and missing self for method

B. Wrong folder and gemspec name; greet is instance method

C. Correct structure with module and class method greet

D. Method defined outside module, no namespacing

Solution

1. Step 1: Check folder and file structure

   Ruby gems use lib/ folder and a gemspec named after the gem. Correct structure with module and class method greet uses lib/my_gem.rb and my_gem.gemspec, which is correct.

2. Step 2: Verify code correctness

   Correct structure with module and class method greet defines a module MyGem with a class method self.greet returning "Hello!", which is the right way to provide a gem method.

3. Final Answer:

   Correct structure with module and class method greet -> Option C

4. Quick Check:

   lib folder + module + self method = correct gem code [OK]

Hint: Use lib folder and module with self.method for gem code [OK]

Common Mistakes:

• Using wrong folder names like src
• Defining instance instead of class methods
• Not namespacing methods inside a module