Ruby Cheat Sheet

puts "Hello, Ruby"

a = 10
b = "text"
c = true

@instance_var = 1
@@class_var = 2
$global_var = 3

Integer
Float
String
Symbol
Array
Hash
Boolean
NilClass

10.class
"text".class

s = "Ruby"

s.length
s.upcase
s.include?("Ru")

name = "World"
"Hello #{name}"

:key
:name

:key.object_id

a + b
a - b
a * b
a / b
a % b

a == b
a != b
a > b
a < b

a && b
a || b
!a

if a > 10
  "large"
elsif a > 5
  "medium"
else
  "small"
end

case a
when 1
  "one"
when 2
  "two"
else
  "other"
end

for i in 1..5
  puts i
end

while a > 0
  a -= 1
end

5.times do |i|
  puts i
end

def add(a, b)
  a + b
end

add(2, 3)

def multiply(a, b = 2)
  a * b
end

def total(*nums)
  nums.sum
end

arr = [1, 2, 3]
arr << 4
arr[0]

arr.map { |n| n * 2 }
arr.select { |n| n > 1 }
arr.find { |n| n == 2 }

h = { a: 1, b: 2 }

h[:a]
h[:b] = 3

arr.each do |item|
  puts item
end

h.each do |k, v|
  puts "#{k}: #{v}"
end

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

[1, 2, 3].map do |n|
  n * 2
end

proc_obj = Proc.new { |x| x * 2 }
lambda_obj = ->(x) { x * 2 }

proc_obj.call(5)
lambda_obj.call(5)

class Counter
  def initialize
    @value = 0
  end

  def increment
    @value += 1
  end

  def value
    @value
  end
end

class Animal
  def speak; end
end

class Dog < Animal
end

module MathUtil
  def add(a, b)
    a + b
  end
end

class Box
  include MathUtil
end

module Loggable
  def log(msg)
    puts msg
  end
end

class App
  include Loggable
end

private
protected
public

begin
  raise "error"
rescue => e
  puts e.message
ensure
end

File.write("file.txt", "text")
content = File.read("file.txt")

"key".to_sym
:key.to_s

arr.reduce(0) { |sum, n| sum + n }

arr.any? { |n| n > 2 }
arr.all? { |n| n > 0 }

Time.now

require "json"