Ruby Quick Reference

puts "Hello"

p value  # inspect

name = "Ada"

MAX = 100

a, b = 1, 2

name = gets.chomp

"42".to_i

3.to_s

"3.5".to_f

:sym.to_s

user&.address&.city

name ||= "guest"

"Hi #{name}, you are #{age}"

s.upcase

s.strip

s.length

s.reverse

s.include?("ru")

s.start_with?("http")

s.sub("a", "b")

s.gsub(/\d/, "#")

s.split(",")

words.join(", ")

format("%.2f", price)

nums = [3, 1, 2]

nums << 4

nums.push(5)

nums.first

nums.last

nums[1..2]

nums.map { |n| n * 2 }

nums.select(&:even?)

nums.reject(&:zero?)

nums.sum

nums.max

nums.reduce(:+)

nums.sort

users.sort_by(&:age)

nums.sort.reverse

nums.find { |n| n > 1 }

nums.include?(3)

nums.any?(&:negative?)

nums.uniq

nested.flatten

nums.reverse

nums.reverse!  # in place

names.each_with_index { |name, i| puts "#{i}: #{name}" }

users.group_by(&:role)

words.tally

user = { name: "Ada", age: 36 }

user[:name]

user.fetch(:email, "n/a")

user[:email] = "ada@example.com"

user.each { |key, value| puts "#{key}: #{value}" }

user.transform_values(&:to_s)

prices.select { |_, v| v > 10 }

a.merge(b)

user.keys

user.key?(:name)

if x > 0 then ... elsif x == 0 then ... else ... end

puts "ok" unless failed

case status
when :ok then "Success"
when :err then "Failed"
else "Unknown"
end

5.times { |i| puts i }

(1..10).each { |i| }

while running do ... end

def greet(name = "world")
  "Hello, #{name}"
end

def create(name:, admin: false)
end
create(name: "Ada")

def twice
  yield
  yield
end
twice { puts "hi" }

square = ->(n) { n * n }
square.(4)

class Dog
  attr_reader :name

  def initialize(name)
    @name = name
  end

  def bark = "Woof"
end

class Puppy < Dog; end

module Greetable
  def greet = "Hi #{name}"
end
class Dog
  include Greetable
end

Point = Struct.new(:x, :y)

Point = Data.define(:x, :y)

begin
  risky
rescue ArgumentError => e
  puts e.message
ensure
  cleanup
end

raise ArgumentError, "bad input"

File.read("in.txt")

File.write("out.txt", text)

gem install rails

bundle install

bundle exec rspec