Ruby Tutorial

Disclaimer: I don't consider myself an expert of Ruby. I am an eternal student. But, what I describe here should be basic enough to get people going and hopefully be a reference site. I also assume audience has some prior programming knowledge.

Getting Ready

Install Ruby

Mac Users

Best way is to use RVM to install Ruby. If you need to specify Ruby version number, do so by adding the version like this: --ruby=1.9.3.

\curl -sSL https://get.rvm.io | bash -s stable --ruby=1.9.3

Windows Users

http://rubyinstaller.org/downloads/

irb

This is your best friend. Use it to test and try different things. When you develop in Ruby on Rails, rails console will give you the same feel and it will also give you access to all classes in your code.

$ irb
1.9.3-p194 :001 > puts "Hello World"
Hello World
 => nil

Basic Ruby Idioms and Styleguide

https://github.com/styleguide/ruby

• Use came case for class names
• Use snake case for method and variable names

class RubyClassName
  def this_is_method_name
    variable_name = "whatever"
  end
end

• Write expressive method names (Rubyist should be able to get a sense of what methods do without extensive documentation)

# Bad
def number
end

# Good
def get_squared_number
end

• Use ? at the end of method if it returns truthy or falsy value

def is_even?(num)
  num % 2 == 0
end

• Ruby method return whatever was evaluated last, so for simple method, don't use return keyword.

# Bad
def double_the_num(num)
  product = num**2
  return product
end

# Good
def double_the_num(num)
  num**2
end

• Use ||= to check for nil value and initialize a variable

# Bad
a = "something" if a.nil?

# Good
a ||= "something"

• Don't use === for conditions or to check types. === is used for case/switch statement.

Basics

Everything is an object

Literally, everything.

https://www.youtube.com/watch?v=F9GVKxSiQVM

$ irb
1.9.3-p194 :002 > "string".class
 => String
1.9.3-p194 :003 > 1.class
 => Fixnum
1.9.3-p194 :004 > 1.5.class
 => Float
1.9.3-p194 :005 > [1,2,3].class
 => Array
1.9.3-p194 :006 > {}.class
 => Hash
1.9.3-p194 :013 > String.superclass
 => Object
1.9.3-p194 :014 > Object.superclass
 => BasicObject
1.9.3-p194 :015 > BasicObject.superclass
 => nil
1.9.3-p194 :016 > nil.class
 => NilClass

Variables

Ruby variable names do not need any keyword prefix.

variable = "normal variable"

Except the following cases:

$variable = "global variable" : Global variable

@@variable = "class variable" : Class variable

@variable = "instance variable": Instance variable

VARIABLE = "constants" : Constant variable

Standard Output (STDOUT)

• puts adds a carriage return at the end
• print does not add a carriage return at the end
• "#{}" means evaluate what's inside {}. It only works with double-quotes. It doesn't work with single-quotes.

1.9.3-p194 :051 > print "Hello World"
Hello World => nil
1.9.3-p194 :052 > puts "Hello World"
Hello World
 => nil
1.9.3-p194 :053 > a = "Hello World"
 => "Hello World"
1.9.3-p194 :054 > puts "#{a} is what I say"
Hello World is what I say
 => nil
1.9.3-p385 :027 > puts '#{a} is not what I say'
#{a} is not what I say
 => nil

Basic Data Structures

Array

1.9.3: http://www.ruby-doc.org/core-1.9.3/Array.html

2.1.1: http://www.ruby-doc.org/core-2.1.1/Array.html

Mutable and can contain different types of data.

1.9.3-p194 :017 > a = Array.new
 => []
1.9.3-p194 :019 > b = []
 => []
1.9.3-p194 :022 > b << "1"
 => ["1"]
1.9.3-p194 :023 > b << 2
 => ["1", 2]
1.9.3-p194 :024 > b.push(:c => "d")
 => ["1", 2, {:c=>"d"}]
1.9.3-p194 :028 > b << {:d => "e"}
 => ["1", 2, {:c=>"d"}, {:d=>"e"}]
1.9.3-p194 :029 > b.pop
 => {:d=>"e"}
1.9.3-p194 :030 > b
 => ["1", 2, {:c=>"d"}]


1.9.3-p194 :031 > b.length
 => 3
1.9.3-p194 :032 > b.first
 => "1"
1.9.3-p194 :033 > b.last
 => {:c=>"d"}
1.9.3-p194 :034 > b[0]
 => "1"
1.9.3-p194 :035 > b[-1]
 => {:c=>"d"}  

Hash

1.9.3: http://www.ruby-doc.org/core-1.9.3/Hash.html

2.1.1: http://www.ruby-doc.org/core-2.1.1/Hash.html

=> is called hash rocket.

1.9.3-p194 :036 > a = Hash.new
 => {}
1.9.3-p194 :037 > b = {}
 => {}
1.9.3-p194 :039 > c = Hash.new([])
 => {}
1.9.3-p194 :040 > a[:a]
 => nil
1.9.3-p194 :041 > a[:a] = "a"
 => "a"
1.9.3-p194 :042 > a
 => {:a=>"a"}
1.9.3-p194 :043 > b[:a] = "b"
 => nil
1.9.3-p194 :045 > c[:a]
 => []
1.9.3-p194 :047 > c.size
 => 0
1.9.3-p194 :048 > a.size
 => 1
1.9.3-p194 :049 > a[:a]
 => "a"

Use symbol for hash keys to save memory space.

Creating same string creates new object each time, but symbol doesn't.

1.9.3-p385 :014 > a = "blah"
 => "blah"
1.9.3-p385 :015 > a.object_id
 => 70297014082880
1.9.3-p385 :016 > b = "blah"
 => "blah"
1.9.3-p385 :017 > b.object_id
 => 70297013950380
1.9.3-p385 :018 > a.object_id == b.object_id
 => false
1.9.3-p385 :019 > a == b
 => true
1.9.3-p385 :020 > c = :blah
 => :blah
1.9.3-p385 :021 > c.object_id
 => 667848
1.9.3-p385 :022 > d = :blah
 => :blah
1.9.3-p385 :023 > d.object_id
 => 667848
1.9.3-p385 :024 > c == d
 => true
1.9.3-p385 :025 > c.object_id == d.object_id
 => true

Basic Control Structure

If, elsif, else

if condition_a
  do_something
elsif condition_b
  do_something_else
else
  do_yet_another
end

But if you only care about one condition use single line.

do_something if condition_a

Unless

Don't use unless with else.

# Bad
unless condition_a
  do_something
else
  do_something_else
end

# Good
do_something_else unless condition_b

Iteration

Enumerable, 1.9.3: http://ruby-doc.org/core-1.9.3/Enumerable.html

Enumerable, 2.1.1: http://ruby-doc.org/core-2.1.1/Enumerable.html

In Ruby, most iterations happen over a collection of elements and you pass block that will be iterated on each element. Enumerable mixin or module provides a lot more functionalities than standard Array/Hash methods. Enumerable methods work both on arrays and hashes.

Use do/end if multiple lines are required. Use {} for single line.

numbers = [1, 2, 3]

numbers.each do |num|
  puts num**2
  puts num
end

numbers.each { |num| puts num }

hash = {:a => "A", :b => "B"}

hash.each { |key, value| puts "#{hash[key]} = #{value}" }

Working with HTTP request/response

Net::HTTP, 1.9.3: http://www.ruby-doc.org/stdlib-1.9.3/libdoc/net/http/rdoc/Net/HTTP.html

JSON, 1.9.3 : http://ruby-doc.org/stdlib-1.9.3/libdoc/json/rdoc/JSON.html

Net::HTTP, 2.1.1: http://www.ruby-doc.org/stdlib-2.1.1/libdoc/net/http/rdoc/Net/HTTP.html

JSON, 2.1.1 : http://ruby-doc.org/stdlib-2.1.1/libdoc/json/rdoc/JSON.html

Net::HTTP, URI, and JSON are part of stanard libraries in Ruby. To use them, you need to require them first.

Examples can be found here: http://www.rubyinside.com/nethttp-cheat-sheet-2940.html

GET

1.9.3-p194 :055 > require 'json'
 => true
1.9.3-p194 :056 > require 'net/http'
 => true
1.9.3-p194 :057 > require 'uri'
 => false
1.9.3-p194 :065 > uri = URI.parse("http://www.google.com")
 => #<URI::HTTP:0x007fb80446efb0 URL:http://www.google.com>
1.9.3-p194 :066 > response = Net::HTTP.get_response(uri)
 => #<Net::HTTPOK 200 OK readbody=true>
1.9.3-p194 :067 > response.code
 => "200"
1.9.3-p194 :068 > response.body
 # Buch of HTML codes
1.9.3-p194 :068 > JSON.parse(response.body)
 # JSON data converted to hash if it contains JSON data

POST

Using form data is easy.

response = Net::HTTP.post_form(uri, {"q" => "My query", "per_page" => "50"})

Using JSON data in body requires more typing

uri = URI.parse('https://myapp.com/api/v1/resource')
req = Net::HTTP::Post.new(uri, initheader = {'Content-Type' =>'application/json'})
req.body = {param1: 'some value', param2: 'some other value'}.to_json
response = Net::HTTP.start(uri.hostname, uri.port) do |http|
  http.request(req)
end

You can also use RestClient gem: https://github.com/rest-client/rest-client

Reading from file

1.9.3: http://ruby-doc.org/core-1.9.3/File.html

2.1.1: http://ruby-doc.org/core-2.1.1/File.html

Use abosolute path to read from file. You can also go each line by line as well. Refer to the links above.

> json = File.read("/pah/to/json/file.json")
> puts json
# output of file content

Executable Ruby Scripts

Just add absolute path to the ruby binary at the top of ruby script and make the script executable.

yangtheman:~/codes/ruby/practices$ whereis ruby
/usr/bin/ruby
yangtheman:~/codes/ruby/practices$ ruby -v
ruby 1.9.3p385 (2013-02-06 revision 39114) [x86_64-darwin12.2.1]

#!/usr/bin/ruby

puts "Hello World"

Classes

• Ruby has only single inheritance.
• Ruby class constructor method is called initialize. It gets called automatically when an instance of a class is created.
• Use attr_reader to make an attribute readable.
• Use attr_writer to make an attribute writable.
• Use attr_accessor to make an attribute both readable/writable.

class SampleClass

  attr_reader :length

  def initialize(len = 10)
    @length = len
  end

end

sample = Sample.new
sample.length # will return 10

• Subclass can be created using <.
• Use super method to access the same method in parent class.

class ChildClass < SampleClass

  def initialize(len = 5)
    super
  end

end

child = ChildClass.new
child.length # will return 5

Modules

• Module serves two purposes: Namespacing and Mixin
• It cannot be instantiated.
• It can be included in a class to make the methods available to an instance or a class.

# Namespacing
Module TopName
  class SomeClass
  end
end

test = TopName::SomeClass.new

# Mixin
Module MoreArrayMethods
  def some_method
  end
end

Class Array
  include MoreArrayMethods
end

class Hash
  extend MoreArrayMethods
end

array = Array.new
array.some_method  # instance method

Hash.some_method # class method
hash = Hash.new
hash.extend MoreArrayMethods
hash.some_method # instance method