💎 Chapter 26 — Ruby Programming Language

Complete reference for Ruby built-in classes and modules — String, Array, Hash, File, Enumerable and more with copy-paste examples.
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⚡ Quick Copy-Paste Examples

Save as .rb file and run with ruby script.rb.

#!/usr/bin/env ruby
def greet(name)
  "Hello, #{name.capitalize}! Ruby #{RUBY_VERSION} on #{RUBY_PLATFORM}"
end
puts greet("world")
puts greet("mywebuniversity")

# Blocks and ranges
(1..5).each { |i| print "#{i}^2=#{i**2}  " }; puts

# One-liner array processing
puts (1..10).select(&:even?).map { |n| n * n }.inspect

# Everything is an expression
result = if Time.now.hour < 12 then "Good morning" else "Good afternoon" end
puts result
# ruby hello.rb

module Describable
  def describe = "#{self.class.name}: #{self}"
end

class Animal
  include Describable
  include Comparable
  attr_accessor :name, :age
  def initialize(name, age) = (@name, @age = name, age)
  def <=>(other) = @age <=> other.age
  def to_s       = "#{@name}(#{@age})"
end

class Dog < Animal
  def speak = "#{@name} says: Woof!"
end

class Cat < Animal
  def speak = "#{@name} says: Meow!"
end

animals = [Dog.new("Rex",3), Cat.new("Luna",7), Dog.new("Max",1), Cat.new("Cleo",5)]
puts animals.sort.map(&:to_s).inspect
puts animals.max.describe
animals.each(&:speak).each { |a| puts a.speak }
# ruby oop_demo.rb

# Proc vs Lambda
square = proc  { |x| x * x }
cube   = lambda { |x| x ** 3 }
double = ->(x) { x * 2 }

[1,2,3,4,5].each { |n| puts "#{n}: sq=#{square.(n)} cu=#{cube.(n)} dbl=#{double.(n)}" }

# Function composition (Ruby 2.6+)
triple   = ->(x) { x * 3 }
add_one  = ->(x) { x + 1 }
pipeline = triple >> add_one
puts (1..5).map(&pipeline).inspect

# yield and block_given?
def repeat(n)
  n.times { yield } if block_given?
end
repeat(3) { print "Ruby! " }; puts

# Memoization with Hash default
fib = Hash.new { |h,n| h[n] = n < 2 ? n : h[n-1] + h[n-2] }
puts (0..10).map { |n| fib[n] }.inspect
# ruby blocks_demo.rb

require "csv"
File.write("students.csv", <<~CSV)
  Name,Subject,Score,Email
  Alice,Math,95,alice@example.com
  Bob,Science,87,bob@example.com
  Carol,Math,92,carol@example.com
  Dave,Science,78,dave@example.com
  Eve,Math,98,eve@example.com
CSV

students = CSV.foreach("students.csv", headers: true).map do |row|
  { name: row["Name"], subject: row["Subject"],
    score: row["Score"].to_i, email: row["Email"] }
end

students.group_by { |s| s[:subject] }.each do |subj, group|
  avg = group.sum { |s| s[:score] }.to_f / group.size
  puts "#{subj}: avg=#{avg.round(1)} top=#{group.max_by{|s|s[:score]}[:name]}"
end

emails = File.read("students.csv").scan(/[\w.+-]+@[\w-]+\.[\w.]+/)
puts "Emails: #{emails.inspect}"
puts "Domains: #{emails.map { |e| e.split("@").last }.uniq.inspect}"
File.delete("students.csv")
# ruby csv_demo.rb

# Threads with Mutex
counter = 0
mutex   = Mutex.new
threads = 10.times.map do |i|
  Thread.new do
    100.times { mutex.synchronize { counter += 1 } }
  end
end
threads.each(&:join)
puts "Counter: #{counter} (expected 1000)"

# Queue (producer-consumer)
require "thread"
queue = Queue.new
producer = Thread.new { 5.times { |i| queue << "item-#{i}"; sleep 0.01 }; queue << :done }
items    = []
consumer = Thread.new { loop { (v = queue.pop) == :done ? break : items << v } }
[producer, consumer].each(&:join)
puts "Consumed: #{items.inspect}"

# Fiber (coroutine)
fib = Fiber.new do
  a, b = 0, 1
  loop { Fiber.yield a; a, b = b, a + b }
end
puts (10.times.map { fib.resume }).inspect
# ruby threads_demo.rb