Ruby

TL;DR

One-liner: Ruby is designed for developer happiness - expressive, elegant, and productive.

Core Strengths:

• Beautiful, readable syntax
• Everything is an object
• Rails framework for rapid web development
• Vibrant community and rich gems ecosystem

Philosophy

Ruby follows the principle of least surprise:

• Optimized for developer happiness - Matz designed Ruby to be fun to use
• Everything is an object - Even numbers and nil have methods
• Duck typing - If it walks like a duck, it’s a duck
• Convention over configuration - Sensible defaults, less boilerplate

Ruby values expressiveness over performance. It’s a language where you write what you mean.

Quick Start

Install

# macOS
brew install ruby

# Linux - use version manager (recommended)
curl -fsSL https://github.com/rbenv/rbenv-installer/raw/HEAD/bin/rbenv-installer | bash
rbenv install 3.4.8
rbenv global 3.4.8

Verify (latest: 3.4.8)

ruby --version  # ruby 3.4.8

First Program

Create hello.rb:

puts "Hello, World!"

ruby hello.rb

Interactive Ruby (IRB)

irb
>> 2 + 2
=> 4
>> "hello".upcase
=> "HELLO"

Language Essentials

Variables & Types

# Variables (no type declarations)
name = "Alice"
age = 25
price = 19.99
active = true

# Symbols (immutable identifiers)
status = :pending

# Arrays
numbers = [1, 2, 3]
mixed = [1, "two", :three]

# Hashes (dictionaries)
user = { name: "Alice", age: 25 }
user[:name]  # "Alice"

Control Flow

# if-else
if age >= 18
  puts "Adult"
elsif age >= 13
  puts "Teen"
else
  puts "Child"
end

# One-liner
puts "Adult" if age >= 18

# unless (opposite of if)
puts "Minor" unless age >= 18

# case (pattern matching)
case status
when :pending
  "Waiting"
when :active, :running
  "In progress"
else
  "Unknown"
end

Iterators & Blocks

# Blocks are everywhere
5.times { puts "Hello" }

# each
[1, 2, 3].each { |n| puts n }

# map
doubled = [1, 2, 3].map { |n| n * 2 }  # [2, 4, 6]

# select (filter)
evens = [1, 2, 3, 4].select { |n| n.even? }  # [2, 4]

# Multi-line block
numbers.each do |n|
  puts n * 2
end

Methods

# Method definition
def greet(name)
  "Hello, #{name}!"  # Implicit return
end

# Default parameters
def greet(name, greeting = "Hello")
  "#{greeting}, #{name}!"
end

# Keyword arguments
def create_user(name:, age:, admin: false)
  { name: name, age: age, admin: admin }
end

create_user(name: "Alice", age: 25)

Classes

class User
  attr_accessor :name, :age  # Getters and setters

  def initialize(name, age)
    @name = name  # Instance variable
    @age = age
  end

  def adult?
    @age >= 18
  end
end

user = User.new("Alice", 25)
user.name       # "Alice"
user.adult?     # true

Gotchas

nil is falsy, but 0 and "" are truthy

if nil
  # won't run
end

if 0
  puts "0 is truthy!"  # Will print!
end

if ""
  puts "empty string is truthy!"  # Will print!
end

Symbols vs Strings

# Symbols are immutable and memory-efficient
:name.object_id == :name.object_id  # true

# Strings are mutable
"name".object_id == "name".object_id  # false

# Use symbols for hash keys
user = { name: "Alice" }  # Symbol key
user[:name]               # Access with symbol

Implicit return

def add(a, b)
  a + b  # Last expression is returned
end

# Explicit return only when needed
def early_exit(n)
  return "negative" if n < 0
  n * 2
end

Method naming conventions

# ? for predicates (return boolean)
"hello".empty?    # false
[1, 2].include?(1)  # true

# ! for dangerous/mutating methods
str = "hello"
str.upcase   # Returns "HELLO", str unchanged
str.upcase!  # Modifies str in place

When to Choose

Best for:

• Web applications (Ruby on Rails)
• Rapid prototyping
• Scripting and automation
• Startups needing fast development

Not ideal for:

• Performance-critical applications
• Mobile development
• Data science (use Python)

Comparison:

Aspect	Ruby	Python	JavaScript
Web framework	Rails	Django	Express
Syntax	Elegant	Clean	Flexible
Speed	Slow	Medium	Medium
Use case	Web	General	Full-stack

Next Steps

• Ruby Documentation
• Ruby in 20 Minutes
• Ruby on Rails
• RubyGems

Ecosystem

Package Management

gem install rails       # Install a gem
gem list                # List installed gems
bundle init             # Create Gemfile
bundle install          # Install dependencies

Popular Gems

• Web: Rails, Sinatra, Hanami
• Testing: RSpec, Minitest
• Database: ActiveRecord, Sequel
• Background jobs: Sidekiq, Resque