Ruby Crash Course

Objectives

• Describe the history of the Ruby language
• Identify fundamentals and concepts of the Ruby langauge
• Utilize different primitive types, control structures, and methods in Ruby

Humble Origins

Ruby is an object-oriented language suitable for writing day to day scripts as well as full-scale applications. Yukihiro Matsumoto, or "Matz", began work on Ruby back in 1993, because he wanted a language that made him productive while being fun to use. Initially popular in Japan, Ruby has been finding its way into the hearts of programmers all over the world.

• Ruby stylistically conforms to the snake_case convention
• The documentation is fantastic

Further reading: The Philosophy of Ruby

Yukihiro Matsumoto

Why JavaScript, then Ruby?

While Ruby is a general purpose language that can be used for many purposes, we'll be applying it to a web development framework called Rails. We learned JavaScript first because it's the only language that runs natively in browsers, and we'll be utilizing some JavaScript for our front-end code, while utilizing Ruby for our back-end code.

You'll also find that while Ruby is a functional language, functions cannot be passed into other functions (functions are not first-class citizens). However, its object-oriented capabilities and clean syntax provide different strengths as a language. The widely used Rails framework also provides an opinionated development workflow, which can lead to faster development.

Comments

In JS, we use line and multiline comments.

// here's a line comment

/* And a multiline
   comment
*/

In Ruby, multiline comments exist, but we generally use line comments with hashtags, for readability.

# here is a line comment

# here is a block
# of comments
# for you to read

Variables

Local variables start with a lowercase letter. No var necessary.

my_variable = 5
puts my_variable
#=> 5

Constants

Mostly, we're able to change what a variable's holding if we so choose – constants are designed for the opposite. Constants are meant to be placeholders that never change.

SOME_CONSTANT = 'donuts'
#=> "donuts"

SOME_CONSTANT = 'awesome'
#=> warning: already initialized constant SOME_CONSTANT

Note that if we try to reassign a constant, the reassignment still succeeds! All the constant syntax does is throw an error on reassignment.

Data Types

Nothingness

Just as Javascript uses undefined or null, ruby uses nil

my_bank_account = nil

Booleans

A binary representation: either true or false

is_operating = true
is_broken = false

Numbers

Datatypes used to represent a number

• Fixnum: 23
• Bignum: 23238923859348534535
• Float: 23.23

Strings

A primative datatype used to represent a string of characters

Methods

.split
.index
.upcase
.downcase
.sub
.gsub
.capitalize

Examples

person = 'instructor'

person.split('')
#=> ["i", "n", "s", "t", "r", "u", "c", "t", "o", "r"]

person.index('tr')
#=> 3

person.upcase
#=> "INSTRUCTOR"

person.downcase
#=> "instructor"

person.sub('r', 'a')
#=> "instauctor"
# note that only the first character is replaced

person.gsub('r', 'a')
#=> "instauctoa"
# note that all character instances are replaced

person.capitalize
#=> "Instructor"

person.reverse
#=> "rotcurtsni"

person.length
#=> 10

Operators

+
-
/
*
** #exponent
% #modulo

+=
-=
*=
/=
**=

==
!=
!
||
&&

Note that Ruby has a === operator, BUT the operator means something different in Ruby. We'll touch on this when we get to ranges. You can use the .equal? function as an identity operator.

Arrays

An indexed arrangement of objects

several ways to create an array

arr = [1,2,3]
#=> [1,2,3]
arr1 = Array.new([4,5,6])
#=> [4,5,6]
arr2 = Array.new(3, true)
#=> [true, true, true]

Array Methods

.sort
.reverse
.concat
.length
.push # (<<)
.shuffle
.shift
.unshift
.slice # (negative indicies or ranges, use ! to "splice")
.first
.last
.delete
.delete_at
.inspect

Examples

numbers = [4, 2, 3, 1]

numbers.sort
# => [1, 2, 3, 4]

numbers.reverse
# => [1, 3, 2, 4]

numbers.concat([5, 6, 7])
# => [4, 2, 3, 1, 5, 6, 7]

numbers.length
# => 7

numbers.push(8)
# => [4, 2, 3, 1, 5, 6, 7, 8]

numbers << 9
# => [4, 2, 3, 1, 5, 6, 7, 8, 9]

numbers.shuffle
# => output will vary

numbers.shift
# => 4
numbers
# => [2, 3, 1, 5, 6, 7, 8, 9]

numbers.unshift(4)
# => [4, 2, 3, 1, 5, 6, 7, 8, 9]

numbers.slice(0, 2)
# => [4, 2]
numbers
# => [4, 2, 3, 1, 5, 6, 7, 8, 9]

numbers.slice!(0, 2)
# => [4, 2]
numbers
# => [3, 1, 5, 6, 7, 8, 9]

numbers.first
# => 3

numbers.last
# => 9

numbers << 'a'
# => [3, 1, 5, 6, 7, 8, 9, "a"]
numbers.delete('a')
# => "a"
numbers
# => [3, 1, 5, 6, 7, 8, 9]

numbers.delete_at(0)
# => 3
numbers
# => [1, 5, 6, 7, 8, 9]

Ranges

A set of values with a beginning and an end Specfiically this uses ..to set a range between two values A and B A..B

a_range = (1..10) # includes 10
another_range = (1...10) # not including 10
letters_range = ('a'..'z')

typecasting in action

another_range.to_a
=> [1,2,3,4,5,6,7,8,9]

Using === to determine if an element is within a range or set

another_range === 3
#=> true

=== can also be used to check whether something is part of a type or in encapsulated in a regular expression.

Integer === 5
# => true
Integer === 'hello'
# => false

/air/ === 'Hair'
# => true
/air/ === 'Bald'
# => false

### Symbols
An immutable sequence of characters that represents data stored in a specific memory location. Symbols optimize memory and can help programs run faster when performing comparisons or lookups.

```ruby
country = :turkey
food = :turkey

country.object_id == food.object_id
=> true

country = 'turkey'
food = 'turkey'

country.object_id == food.object_id
=> false

Hashes

A hash consists of unindexed key-value pairs. You may construct a hash in either of the following ways. Each will use symbols.

dog = {
  :name => 'Hamlet',
  :breed => 'Pug',
  :fav_food => 'pate'
}
cat = {
  name: 'Simba',
  breed: 'American Shorthair',
  fav_food: 'Prosciutto'
}
dog[:name]
=> 'Hamlet'
cat[:fav_food]
=> 'Prosciutto'

Mutator methods !

Mutator methods will not just return a value, but change the object they are called on to that value. Adding ! to certain ruby methods will turn them into their mutator method counterparts. Some people call these "methods with a bang" for self-explanatory reasons!

How to mutate an array

arr = [7,4,5]
arr.sort #not a mutator method
# => [4,5,7]
arr
# => [7,4,5]

arr = [7,4,5]
arr.sort! #the '!', aka a 'bang' will mutate the object
# => [4,5,7]
arr
# => [4,5,7]

Typecasting

Typecasting is the act of altering an object's datatype

.to_i
.to_s
.to_a
.to_f

Code blocks

You can use curly braces, { } for single line blocks and do ... end for multiline blocks.

We will almost exclusively be using do ... end.

# count to 10
10.times { puts "Hello" }

x = 0
until x > 10 do
  puts x
  x += 1
end

String Interpolation

Allows one to inlcude a dynamic variable in a string. String interpolation can only be done on double-quoted strings.

team = 'Mariners'
puts "Go #{team}!"
# => "Go Mariners!"

Control flow

• Conditionals

if
elsif
else
unless

• Loops

until
while
times
for

• Enumerables (similar to iterators)

each
each_char # for strings
each_index
map
select
reduce

Examples

If/Else

course = "wdi"
if course == "uxdi"
  puts "Hello, User Experience Designer!"
elsif course == "fewd"
  puts "Hello, Front-End Developer"
elsif course == "wdi"
  puts "Hello, Immersed Student"
else
  puts "Who are you?"
end

Inline conditional

if heroic
  do_something_heroic
end

# is the same as
do_something_heroic if heroic == true

# is the same as
do_something_heroic if heroic

Loops

i = 0
while i < 5 do
  puts "i is " + i.to_s
  i += 1
end

# is the same as
i = 0
until i == 5 do
  puts "i is " + i.to_s
  i += 1
end

# is the same as
5.times do |i|
  puts "i is #{i}"
end

# is the same as
for i in (0...5) do
  puts "i is " + i.to_s
end


# Will print out:
# >i is 0
# >i is 1
# >i is 2
# >i is 3
# >i is 4

Iterating through Arrays

foods = ["carrots", "kale", "beets"]
foods.each do |vegetable|
  puts "i like #{vegetable}"
end

# is the same as
for veg in ["carrots", "kale", "beets"] do
  puts "i like #{veg}"
end

# printing out indices
foods.each_with_index do |vegetable, i|
  puts "i like #{vegetable}, #{i}"
end

# Will _each_ print out:
# >i like carrots, 0
# >i like kale, 1
# >i like beets, 2

Enumerables

foods = ['carrots', 'kale', 'beets']

# map (similar to JS map)
foods.map do |food|
  food * 2
end
# => ["carrotscarrots", "kalekale", "beetsbeets"]


# select (similar to JS filter)
foods.select do |food|
  ['carrots', 'kale'].include?(food)
end
# => ["carrots", "kale"]

# reduce (similar to JS reduce)
numbers = [1, 2, 3, 4]
numbers.inject do |a, b|
  a + b
end
# => 10

# reduce with a starting value
numbers.reduce(10) do |a, b|
  a + b
end

# reduce applying an operation/function via a symbol
numbers.reduce(:+)

Iterating through Hashes

car = {wheels: 4, doors: 2, seats: 5}
car.each do |key, num|
  puts "my car has #{num} #{key}"
end

# Will print out:
# my car has 4 wheels
# my car has 2 doors
# my car has 5 seats

Functions

In Javascript

• anonymous: function (param1, [..param2, [...]]){...},
• named: function Name(param1, [..param2, [...]]){...}
• uses lexical scope
• used as values (functional programming)
• require explicit return
• all params are optional

In Ruby

• uses def
• does not capture scope
• not used as values
• implicitly returns last evaluation
• optional parameters must be specified

Examples

def say_hello
  puts "Hello, World!"
end

say_hello()

# is the same as

def say_hello
  puts "Hello, World!"
end

# note missing parentheses
say_hello

In Ruby, leaving the () off of a function call is possible. Since functions can't be passed as values (i.e., aren't first-class), Ruby knows that we mean to call the function, so it calls it.

Parameters (Arguments)

def say_hello(friend)
  puts "Hello, #{friend}!"
end

say_hello("Tim")

# is the same as
def say_hello(friend)
  puts "Hello, #{friend}!"
end

# note the lack of parentheses
say_hello "Tim"

Keyword Arguments

def say_hello(friend: 'Tim')
  puts "Hello, #{friend}!"
end

# note that there are no arguments
say_hello

Return Values

def add(num1, num2)
  return num1 + num2
end

sum = add(2, 3)
puts "2 + 3 = #{sum}"

# is the same as
def add(num1, num2)
  # note the lack of explicit return
  num1 + num2
end

sum = add(2, 3)
puts "2 + 3 = #{sum}"

Ruby will automatically return the value of the last evaluated expression. This is called having "implicit returns". You are free to have an explicit return statement, but you don't have to.

Input / Output

You've already seen how puts will output information to the screen. What if we want to accept user input? Let's try gets.

puts "Enter your name:"
you = gets

puts "Enter a friend's name:"
friend = gets

puts "Hello, #{friend}. #{you} says hi."

# Outputs
# Enter your name:
# Tim
# Enter a friend's name:
# Bob
# Hello, Bob
# . Tim
#  says hi.

That almost works as we want, but gets is reading in the newline character from when we pressed the Enter key. Generally, when reading user input we want to chomp the data. (See http://www.ruby-doc.org/docs/Tutorial/part_02/user_input.html)

puts "Enter your name:"
you = gets.chomp

puts "Enter a friend's name:"
friend = gets.chomp

puts "Hello, #{friend}. #{you} says hi."

# Enter your name:
# Tim
# Enter a friend's name:
# Frank
# Hello, Frank. Tim says hi.

Much better. Now the unnecessary newlines are removed, thanks to chomp.

ARGV

If we want to run a ruby script from the command line, we can get command line arguments with ARGV

It works much like process.argv

Try it:

touch banana.rb

Edit the file and put this inside:

puts "helloe world"

Run it.

ruby banana.rb

Edit the file to puts the command line arguments:

puts "helloe world #{ARGV[0]}"

Run it

ruby banana.rb monkey

JSON

In ruby, if you want to work with a file, it's very simple.

Use the built-in File library to read in the data. It's sychronous.

file = File.read('products.json')

The thing you get is one big string, so you need to parse it:

data = JSON.parse(file)