1 files changed, 145 insertions, 56 deletions

diff --git a/ruby.html.markdown b/ruby.html.markdown
index 962853a2..3eed2d3c 100644
--- a/ruby.html.markdown
+++ b/ruby.html.markdown
@@ -9,7 +9,12 @@ contributors:
   - ["Nick LaMuro", "https://github.com/NickLaMuro"]
   - ["Marcos Brizeno", "http://www.about.me/marcosbrizeno"]
   - ["Ariel Krakowski", "http://www.learneroo.com"]
-
+  - ["Dzianis Dashkevich", "https://github.com/dskecse"]
+  - ["Levi Bostian", "https://github.com/levibostian"]
+  - ["Rahil Momin", "https://github.com/iamrahil"]
+  - ["Gabriel Halley", "https://github.com/ghalley"]
+  - ["Persa Zula", "http://persazula.com"]
+  - ["Jake Faris", "https://github.com/farisj"]
 ---
 
 ```ruby
@@ -35,7 +40,13 @@ You shouldn't either
 8 - 1 #=> 7
 10 * 2 #=> 20
 35 / 5 #=> 7
-2 ** 5 #=> 32
+2**5 #=> 32
+5 % 3 #=> 2
+
+# Bitwise operators
+3 & 5 #=> 1
+3 | 5 #=> 7
+3 ^ 5 #=> 6
 
 # Arithmetic is just syntactic sugar
 # for calling a method on an object
@@ -43,7 +54,7 @@ You shouldn't either
 10.* 5 #=> 50
 
 # Special values are objects
-nil # Nothing to see here
+nil # equivalent to null in other languages
 true # truth
 false # falsehood
 
@@ -58,8 +69,6 @@ false.class #=> FalseClass
 # Inequality
 1 != 1 #=> false
 2 != 1 #=> true
-!true  #=> false
-!false #=> true
 
 # apart from false itself, nil is the only other 'falsey' value
 
@@ -73,22 +82,57 @@ false.class #=> FalseClass
 2 <= 2 #=> true
 2 >= 2 #=> true
 
+# Combined comparison operator
+1 <=> 10 #=> -1
+10 <=> 1 #=> 1
+1 <=> 1 #=> 0
+
+# Logical operators
+true && false #=> false
+true || false #=> true
+!true #=> false
+
+# There are alternate versions of the logical operators with much lower
+# precedence. These are meant to be used as flow-control constructs to chain
+# statements together until one of them returns true or false.
+
+# `do_something_else` only called if `do_something` succeeds.
+do_something() and do_something_else()
+# `log_error` only called if `do_something` fails.
+do_something() or log_error()
+
+
 # Strings are objects
 
 'I am a string'.class #=> String
 "I am a string too".class #=> String
 
-placeholder = "use string interpolation"
+placeholder = 'use string interpolation'
 "I can #{placeholder} when using double quoted strings"
 #=> "I can use string interpolation when using double quoted strings"
 
+# Prefer single quoted strings to double quoted ones where possible
+# Double quoted strings perform additional inner calculations
+
 # Combine strings, but not with numbers
-"hello " + "world"  #=> "hello world"
-"hello " + 3 #=> TypeError: can't convert Fixnum into String
-"hello " + 3.to_s #=> "hello 3"
+'hello ' + 'world'  #=> "hello world"
+'hello ' + 3 #=> TypeError: can't convert Fixnum into String
+'hello ' + 3.to_s #=> "hello 3"
+
+# Combine strings and operators
+'hello ' * 3 #=> "hello hello hello "
+
+# Append to string
+'hello' << ' world' #=> "hello world"
 
-# print to the output
+# print to the output with a newline at the end
 puts "I'm printing!"
+#=> I'm printing!
+#=> nil
+
+# print to the output without a newline
+print "I'm printing!"
+#=> I'm printing! => nil
 
 # Variables
 x = 25 #=> 25
@@ -130,11 +174,12 @@ array = [1, 2, 3, 4, 5] #=> [1, 2, 3, 4, 5]
 
 # Arrays can contain different types of items
 
-[1, "hello", false] #=> [1, "hello", false]
+[1, 'hello', false] #=> [1, "hello", false]
 
 # Arrays can be indexed
 # From the front
 array[0] #=> 1
+array.first #=> 1
 array[12] #=> nil
 
 # Like arithmetic, [var] access
@@ -145,19 +190,29 @@ array.[] 12 #=> nil
 
 # From the end
 array[-1] #=> 5
+array.last #=> 5
 
 # With a start index and length
 array[2, 3] #=> [3, 4, 5]
 
+# Reverse an Array
+a=[1,2,3]
+a.reverse! #=> [3,2,1]
+
 # Or with a range
 array[1..3] #=> [2, 3, 4]
 
 # Add to an array like this
 array << 6 #=> [1, 2, 3, 4, 5, 6]
+# Or like this
+array.push(6) #=> [1, 2, 3, 4, 5, 6]
+
+# Check if an item exists in an array
+array.include?(1) #=> true
 
 # Hashes are Ruby's primary dictionary with keys/value pairs.
 # Hashes are denoted with curly braces:
-hash = {'color' => 'green', 'number' => 5}
+hash = { 'color' => 'green', 'number' => 5 }
 
 hash.keys #=> ['color', 'number']
 
@@ -170,21 +225,25 @@ hash['nothing here'] #=> nil
 
 # Since Ruby 1.9, there's a special syntax when using symbols as keys:
 
-new_hash = { defcon: 3, action: true}
+new_hash = { defcon: 3, action: true }
 
 new_hash.keys #=> [:defcon, :action]
 
+# Check existence of keys and values in hash
+new_hash.key?(:defcon) #=> true
+new_hash.value?(3) #=> true
+
 # Tip: Both Arrays and Hashes are Enumerable
 # They share a lot of useful methods such as each, map, count, and more
 
 # Control structures
 
 if true
-  "if statement"
+  'if statement'
 elsif false
-  "else if, optional"
+  'else if, optional'
 else
-  "else, also optional"
+  'else, also optional'
 end
 
 for counter in 1..5
@@ -216,7 +275,7 @@ end
 #=> iteration 5
 
 # You can also surround blocks in curly brackets:
-(1..5).each {|counter| puts "iteration #{counter}"}
+(1..5).each { |counter| puts "iteration #{counter}" }
 
 # The contents of data structures can also be iterated using each.
 array.each do |element|
@@ -226,6 +285,12 @@ hash.each do |key, value|
   puts "#{key} is #{value}"
 end
 
+# If you still need and index you can use "each_with_index" and define an index
+# variable
+array.each_with_index do |element, index|
+  puts "#{element} is number #{index} in the array"
+end
+
 counter = 1
 while counter <= 5 do
   puts "iteration #{counter}"
@@ -237,38 +302,62 @@ end
 #=> iteration 4
 #=> iteration 5
 
+# There are a bunch of other helpful looping functions in Ruby,
+# for example "map", "reduce", "inject", the list goes on. Map,
+# for instance, takes the array it's looping over, does something
+# to it as defined in your block, and returns an entirely new array.
+array = [1,2,3,4,5]
+doubled = array.map do |element|
+  element * 2
+end
+puts doubled
+#=> [2,4,6,8,10]
+puts array
+#=> [1,2,3,4,5]
+
 grade = 'B'
 
 case grade
 when 'A'
-  puts "Way to go kiddo"
+  puts 'Way to go kiddo'
 when 'B'
-  puts "Better luck next time"
+  puts 'Better luck next time'
 when 'C'
-  puts "You can do better"
+  puts 'You can do better'
 when 'D'
-  puts "Scraping through"
+  puts 'Scraping through'
 when 'F'
-  puts "You failed!"
+  puts 'You failed!'
 else
-  puts "Alternative grading system, eh?"
+  puts 'Alternative grading system, eh?'
 end
-
 #=> "Better luck next time"
 
 # cases can also use ranges
 grade = 82
 case grade
-    when 90..100
-      puts "Hooray!"
-    when 80...90
-      puts "OK job" 
-    else
-      puts "You failed!"
+when 90..100
+  puts 'Hooray!'
+when 80...90
+  puts 'OK job'
+else
+  puts 'You failed!'
 end
-
 #=> "OK job"
 
+# exception handling:
+begin
+  # code here that might raise an exception
+  raise NoMemoryError, 'You ran out of memory.'
+rescue NoMemoryError => exception_variable
+  puts 'NoMemoryError was raised', exception_variable
+rescue RuntimeError => other_exception_variable
+  puts 'RuntimeError was raised now'
+else
+  puts 'This runs if no exceptions were thrown at all'
+ensure
+  puts 'This code always runs no matter what'
+end
 
 # Functions
 
@@ -284,23 +373,23 @@ double 3 #=> 6
 
 double double 3 #=> 12
 
-def sum(x,y)
+def sum(x, y)
   x + y
 end
 
 # Method arguments are separated by a comma
 sum 3, 4 #=> 7
 
-sum sum(3,4), 5 #=> 12
+sum sum(3, 4), 5 #=> 12
 
 # yield
 # All methods have an implicit, optional block parameter
 # it can be called with the 'yield' keyword
 
 def surround
-  puts "{"
+  puts '{'
   yield
-  puts "}"
+  puts '}'
 end
 
 surround { puts 'hello world' }
@@ -311,25 +400,25 @@ surround { puts 'hello world' }
 
 
 # You can pass a block to a function
-# "&" marks a reference to a passed block 
+# "&" marks a reference to a passed block
 def guests(&block)
- block.call "some_argument" 
+  block.call 'some_argument'
 end
- 
+
 # You can pass a list of arguments, which will be converted into an array
-# That's what splat operator ("*") is for 
+# That's what splat operator ("*") is for
 def guests(*array)
- array.each { |guest| puts "#{guest}" }
+  array.each { |guest| puts guest }
 end
 
 # Define a class with the class keyword
 class Human
 
   # A class variable. It is shared by all instances of this class.
-  @@species = "H. sapiens"
+  @@species = 'H. sapiens'
 
   # Basic initializer
-  def initialize(name, age=0)
+  def initialize(name, age = 0)
     # Assign the argument to the "name" instance variable for the instance
     @name = name
     # If no age given, we will fall back to the default in the arguments list.
@@ -356,20 +445,19 @@ class Human
   # A class method uses self to distinguish from instance methods.
   # It can only be called on the class, not an instance.
   def self.say(msg)
-    puts "#{msg}"
+    puts msg
   end
 
   def species
     @@species
   end
-
 end
 
 
 # Instantiate a class
-jim = Human.new("Jim Halpert")
+jim = Human.new('Jim Halpert')
 
-dwight = Human.new("Dwight K. Schrute")
+dwight = Human.new('Dwight K. Schrute')
 
 # Let's call a couple of methods
 jim.species #=> "H. sapiens"
@@ -380,7 +468,7 @@ dwight.species #=> "H. sapiens"
 dwight.name #=> "Dwight K. Schrute"
 
 # Call the class method
-Human.say("Hi") #=> "Hi"
+Human.say('Hi') #=> "Hi"
 
 # Variable's scopes are defined by the way we name them.
 # Variables that start with $ have global scope
@@ -399,7 +487,7 @@ defined? @@var #=> "class variable"
 Var = "I'm a constant"
 defined? Var #=> "constant"
 
-# Class also is object in ruby. So class can have instance variables.
+# Class is also an object in ruby. So class can have instance variables.
 # Class variable is shared among the class and all of its descendants.
 
 # base class
@@ -415,7 +503,7 @@ class Human
   end
 end
 
-#  derived class
+# derived class
 class Worker < Human
 end
 
@@ -451,8 +539,8 @@ module ModuleExample
   end
 end
 
-# Including modules binds the methods to the object instance
-# Extending modules binds the methods to the class instance
+# Including modules binds their methods to the class instances
+# Extending modules binds their methods to the class itself
 
 class Person
   include ModuleExample
@@ -467,7 +555,7 @@ Person.new.foo # => 'foo'
 Book.foo       # => 'foo'
 Book.new.foo   # => NoMethodError: undefined method `foo'
 
-# Callbacks when including and extending a module are executed
+# Callbacks are executed when including and extending a module
 
 module ConcernExample
   def self.included(base)
@@ -500,9 +588,10 @@ Something.new.qux # => 'qux'
 
 ## Additional resources
 
-- [Learn Ruby by Example with Challenges](http://www.learneroo.com/modules/61/nodes/338) - A variant of this reference with in-browser challenges. 
+- [Learn Ruby by Example with Challenges](http://www.learneroo.com/modules/61/nodes/338) - A variant of this reference with in-browser challenges.
+- [An Interactive Tutorial for Ruby](https://rubymonk.com/) - Learn Ruby through a series of interactive tutorials.
 - [Official Documentation](http://www.ruby-doc.org/core-2.1.1/)
 - [Ruby from other languages](https://www.ruby-lang.org/en/documentation/ruby-from-other-languages/)
-- [Programming Ruby](http://www.amazon.com/Programming-Ruby-1-9-2-0-Programmers/dp/1937785491/) - An older [free addition](http://ruby-doc.com/docs/ProgrammingRuby/) is available online. 
-
-
+- [Programming Ruby](http://www.amazon.com/Programming-Ruby-1-9-2-0-Programmers/dp/1937785491/) - An older [free edition](http://ruby-doc.com/docs/ProgrammingRuby/) is available online.
+- [Ruby Style Guide](https://github.com/bbatsov/ruby-style-guide) - A community-driven Ruby coding style guide.
+- [Try Ruby](http://tryruby.org) - Learn the basic of Ruby programming language, interactive in the browser.