💎 Learning Ruby

💽 Install

Download Ruby: https://www.ruby-lang.org/en/downloads/
e.g. on Windows: https://rubyinstaller.org/downloads/
Or use TryRuby playground online

👨‍🏫 Learn

• TryRuby online interactive tutorial
• Learn Ruby in One Hour, YouTube video by TechmakerTV

📃 Cheatsheet

• General

  • Parentheses: puts "Hello" is equivalent to puts("Hello")
  • Blocks:
    • do ... end (is equivalent to { ... })
    • begin ... end

• Flow Control

  • if condition ... else ... end e.g. if my_string.empty? print "It's empty" end
  • Ternary: condition ? ... : ...
  • case variable when value; ... else ... end
    e.g. case value when 1; puts "value is 1" when 2; puts "value is 2" else puts "value is neither 1 nor 2" end
  • Loops:
    • loop do ... break ... end
    • for ... in ... end e.g. for i in 1..3; puts i end
    • while/until condition ... end e.g. x = 0; while x <= 10; puts x; x += 1 end
    • begin ... end while/until condition
  • More on Flow Control: Introduction to Programming with Ruby: Flow Control online tutorial by Launch School

• Objects

  • methods array of methods for an object e.g. 1.methods
  • class class of an object e.g. 1.class

• Output

  • "Hello World"
  • puts (adds a new line) e.g. puts "outputs a string", puts 1 + 2, puts [12, 47, 35]
  • print (no new line)
  • << output to a file, append to an array e.g. file << "some text"

• Number class: 1.class, 3.14.class

  • Operators: + * - / **
    Combine with = to assign to variable e.g. x += 3
  • to_s to string e.g. 40.to_s
  • times: Enumerator from 0 to number e.g. 5.times { |i| print i }

• Boolean class: true.class

  • Operators: && ||
  • Quick guide: RubyGuides: Understanding Boolean Values in Ruby

• String class: "my string".class

  • length
  • reverse
  • * to repeat e.g. "Hi " * 5
  • to_i to integer e.g. "23 eggs".to_i
  • gsub global substitute e.g. "I love coding".gsub("coding", "eating")
  • lines to split into an array of lines e.g. "Hi\nHow are you?\n".lines
  • join e.g. "Hi\nHow are you?\n".lines.reverse.join
  • "#{variable}" interpolate variable inside string e.g. "Welcome #{username}!"

• Symbols, similar to enums, e.g. :blue, :red, :id, :name (treated as strings)

• Array class: [].class

  • Example: arr = [12, 47, 35]
  • min, max e.g. [12, 47, 35].min
  • sort and sort! (see Functions/Methods > Conventions section below)
  • [n] access the nth element e.g. arr[0]
  • each e.g. arr.each { |value| puts value }
  • select e.g. arr.select { |value| value > 30 }

• Hash class: {}.class

  • Example: book_dates = {"Title 1": 1983, "Title 2": 2004}
  • new e.g. my_hash = Hash.new {0} would use 0 as the default value for uninitialized keys
  • [key] e.g. books["Awesome Book Title"]
  • keys array of keys
  • values array of values
  • each e.g. book_dates.each { |key, value| puts "#{key} written in #{value}" }
  • select e.g. book_dates.select { |key, value| value == 2004 }

• Functions/Methods:

  • def ... end e.g. def plus_one(value) value + 1 end
  • Conventions:
    • my_function! (excalmation mark) indicates the function modifies the variable
    • my_function? (question mark) indicates the function returns a boolean
  • return my_result
    (if no return specified, function returns the result of the last statement)
  • Parameters
    • Default value e.g. def plus_one(value = 0 ) value + 1 end
    • * variadic function, arguments are in an array e.g. def sum(*values) values.reduce(:+) end
      Calling sum 2, 3, 4 returns 9

• Classes:

  class Book
    attr_accessor :content, :title, :author
  
      def initialize(title, author, content="")
        @title   = title
        @author  = author
        @content = content[0..39]
      end
  
      def to_s
        "#{title} by #{author}"
      end
  end
  
  my_book = Book.new "Awesome Title", "William S.", "Lorem ipsum..."
  puts my_book.content
  puts my_book.to_s