ali-hd/week_10-day_01-ruby

Introduction to Ruby

Lesson Objectives

• Running your Ruby Scripts
• Compare/contrast Ruby and Javascript as programming languages
• Identify specific differences between Ruby and Javascript in the following areas...
  • Variables
  • Fundamental Data Types
  • Data Collections
  • Conditionals
  • Data Immutability
• Explain and apply Ranges
• Interact with symbols and explain their significance

Introduction

Ruby is a server-side language. It was designed and developed in 1995 by Yukihiro "Matz" Matsumoto in Japan.

His philosophy in building Ruby was not about simplicity, but making programming in Ruby feel natural in a way that mirrors life.

This brought about a motto that is common among the Ruby community.

"Matz Is Nice And So We Are Nice"

"Programmers often feel joy when they can concentrate on the creative side of programming, so Ruby is designed to make programmers happy." — Yukihiro "Matz" Matsumoto

Performing everyday tasks, while intricate and complex, come to you naturally.

"Ruby is simple in appearance, but is very complex inside, just like our human body." — Yukihiro "Matz" Matsumoto

Flexibility

Ruby is flexible making it ideal for coding. What this means is that there are no* blackboxes in Ruby. You can open up anything and change it. This could be a powerful tool in the hands of a skilled Rubyist.

Readability

Ruby is hyper readable, the lack of ;, (), keywords like var, return, function mean that your semantic naming of methods and variables combined with the semantic nature of the core library methods result in code that feels more like English than a programming language.

5.times { print "Hi!" }

['grookey', 'scorbunny', 'sobble'].each { |pokemon| print pokemon.capitalize  }

  number = 3
  # => 3

  if( number == 3 ) # with parens
    puts( "It's a 3!" )  
  end  
  # It's a 3!
  # => nil

  if number == 3 # without parens
    puts "It's a 3!"  
  end  
  # It's a 3!
  # => nil

Ruby Basics

Variables

We no longer need to precede new variables with var. Just use the name of the variable!

• Variables are instantiated as they are used

name = "Ebere"

• Written in snake_case. That means all lower case with words separated by underscores.

first_name = "Ebere"

• Variable names should still be semantic
• Variables are still assigned using a single equals sign ( = )

my_favorite_super_hero = "spoderman"
# => "spoderman"

Although we don't use var, there is still syntax to designate whether a variable is local or global.

• Undesignated implies local (e.g., my_number)

my_number = 10

• All-caps implies that your value is constant. Ruby will give you warnings if you try to change the value (e.g., PI = 3.14).

PI = 3.14

puts

puts (short for "put string") is the equivalent of Javascript's console.log()

puts "Hello, Ruby!"
# Hello, Ruby!
# => nil

gets

Ruby also allows us to easily accept inputs from the command line using gets

user_input = gets
# => "My input\n" (Note that this line was typed by the user in the terminal)

user_input
# => "My input\n"

Some notes about gets...

Usually gets is followed by .chomp, which removes the new line generated by the user hitting return If you need to convert your value to a number, add .to_i to the end of the method

Demo

Let's test gets by using it in a Ruby file...

# Run this code in app.rb

# Asks for and stores a command line input into the variable as a string.
puts "How old are you?: "

user_input = gets.chomp.to_i

if user_input > 10
  puts "You are older than ten"
end

# In the terminal from in the same directory as app.rb

$ ruby app.rb
# => How old are you?:
20
# => You are older than ten

$ ruby app.rb
# => How old are you?:

Data Types

Everything Is An Object!

Everything in Ruby is an object.

• By "object" we mean that everything has its own set of properties and methods
• Not a new concept. Some data types in Javascript had their own properties and methods (e.g., string.length)
• You will learn more about this when you dive into Ruby OOP

Numbers

Ruby uses same arithmetic operators as Javascript

• +, -, *, /, %
• Same order of operations too: P.E.M.D.A.S.

1 + 2 # Addition
# => 3

6 - 5 # Subtraction
# => 1

5 * 2 # Multiplication
# => 10

30 / 5 # Division
# => 6

31 / 5 # Note: integer division
# => 6

30 % 5 # Modulo (remainder)
# => 0

31 % 5
# => 1

3 ** 2 # Exponentiation
# => 9

Strings

Words, just like in Javascript.

• Surrounded by single or double-quotes
• Ruby uses similar escape characters
  • Here is a list of them
  • Must instantiate string with double-quotes for escape characters to work

name = "Peter"
# => "Peter"

full_name = "Peter\nParker"
# => "Peter\Parker"

single_quote = 'Peter\nParker'
# => "Peter\Parker"

puts full_name
# Peter
# Parker
# => nil

puts single_quote
# Peter\Parker
# => nil

Not only can you concatenate strings, now you can multiply them too! Remember we couldn't do that in Javascript?

# Concatenation
"Hey " + "there!"
# => "Hey there!"

# Multiplication
"Hey there! " * 3
# => "Hey there! Hey there! Hey there! "

You can concatenate strings but this is NOT recommend.

'ryu' + 'ken' # => 'ryuken'
'ryu' + 2 # => TypeError: no implicit conversion of Integer into String
'ryu' + 2.to_s # => 'ryu2'

Above we see that we can NOT implicitly convert a non-string into a string (unlike what we have seen in JS).

Use single quotes for strings that are not interpolated.

Warning: Backticks are not used for strings! They are used to execute commands.

String Interpolation

Sometimes you will want to print out a string that incorporates a variable. For example...

my_name = "Yassir"
# => "Yassir"

puts "Hi my name is: " + my_name
# Hi my name is: Yassir
# => nil

This works fine. Things aren't so simple when that variable is of a different data type. Like a number...

class_number = 2
# => 2

puts "I am teaching SEI " + class_number
# TypeError: no implicit conversion of Fixnum into String from (pry):26:in `+'

In cases like the above, you either need to convert the variable to a string using .to_s or use something called "interpolation."

• Surround the non-string variable with a hashtag and curly brackets: #{variable}. If you choose this option, you must use double quotes otherwise the interpolation will not work.
• No Javascript equivalent (until ES6 came along)

class_number = 9
# => 9

puts "I am teaching SEI #{class_number}"
# I am teaching SEI 9
# => nil

Booleans

Still true and false.

• We'll be using them in conditionals and comparisons just like in Javascript

Comparison operators in Ruby are nearly identical to Javascript. However, the check for equality is always for both value and data type.

• <, >, <=, >=, ==, !=

Don't worry about === in Ruby for now. It does not have the same application as in Javascript.

Logical operators are also similar.

• !, &&, ||

"Truthiness" and "falsiness" are a lot less complicated in Ruby.

• The only falsey values in Ruby are nil and false

Nil

Ruby's "nothing".

• The equivalent of Javascript's null
• You will usually see it when something does not have a return value (e.g., a puts statement)
• Like in Javascript, nil is falsey

Need to check if something is nil? Use .nil?

NOTE: Any method that ends with a ? means it will return a boolean value.

something = "The Thing"
# => "The Thing"

something.nil?
# => false

something = nil
# => nil

something.nil?
# => true

Operators

You’ll use the following list of operators to do math in Ruby or to compare things. Scan over the list, recognize a few. You know, addition + and subtraction - and so on.

** !  ~  *  /  %  +  -  &
<< >> |  ^  >  >= <  <= <=>
|| != =~ !~ && += -= == ===
.. ... not and or

Conditionals

Pretty similar to Javascript, with some differences.

• No parentheses or curly brackets required
• Begin blocks using if, elsif (no second "e"!) and else
• We close the whole loop using end
  • This will be used throughout Ruby when dealing with code blocks (e.g., method/function) Here's an example where we check for height at a roller coaster...

puts "Welcome to the Iron Rattler! How tall are you (in feet)?"
height = gets.chomp.to_i

if height < 4
  puts "Sorry, you'll fly out of your seat if we let you on."
elsif height < 7
  puts "All aboard!"
else
  puts "If you value your head, you should not get on this ride."
end

if / unless

We also have single-line ifs

puts 'you are old!' if age >= 100

You may even see unless

puts 'you are old!' unless age < 100

When you see an unless foo, read it as if !foo

if !foo can always be written as unless foo which creates a more readable line

Ternary operator

A ternary operator looks just like we have seen in JS condition ? true : false

1 > 2 ? "condition is true" : "condition is false"

A more real life example is:

num.even? ? "#{num} is even!" : "#{num} is odd!"

Same as:

if num.even?
  "#{num} is even!"
else
  "#{num} is odd!"
end

The Bang Symbol (!)

All of the Ruby data types we have discussed so far are mutable.

We can not only change what variables are pointing to in memory, but we can directly modify those values stored in memory as well. Methods with an ! attached to the end of them usually mean that they will modify the value in memory they are being called on.

a = "cheeseburger"
# => "cheeseburger"

a.upcase = "cheeseburger"
# => "CHEESEBURGER"

a
# => "cheeseburger"

a.upcase!
# => "CHEESEBURGER"

Things can get tricky when you have multiple variables pointing at the same value. For example...

a = "cheeseburger"
# => "cheeseburger"

b = a
# => "cheeseburger"

b.upcase!
# => "CHEESEBURGER"

a
# => "CHEESEBURGER"

Data Type Exercise - Lab (30 minutes)

Complete the exercises in this document.

Data Collections

Spend 10 minutes reading through everything up until Hashes.

Arrays

An ordered collection of related values. Same syntax as Javascript arrays.

• Square brackets
• Values separated by commas
• Zero-indexed

numbers = [1, 2, 3]
# => [1, 2, 3]

animals = ["dog", "cat", "horse"]
# => ["dog", "cat", "horse"]

animals[0]
# => "dog"

animals[1] = "elephant"
# => "elephant"

animals
# => ["dog", "elephant", "horse"]

Another super cool Ruby feature is that you can perform arithmetic operations on arrays!

numbers = [1, 2, 3]
# => [1, 2, 3]

more_numbers = [4, 5, 6]
# => [4, 5, 6]

lots_of_numbers = numbers + more_numbers
# => [1, 2, 3, 4, 5, 6]

lots_of_numbers - [4, 5, 6]
# => [1, 2, 3]

numbers * 3
# => [1, 2, 3, 1, 2, 3, 1, 2, 3]

Array Methods

Ruby is very nice. It provides us with an extensive library of array methods we can use to traverse and manipulate arrays.

• The Ruby documentation for Array is a great resource for learning more about these methods.
• Can't go over them all, but chances are if you could do it in Javascript then you can do it in Ruby.

IMPORTANT: You DO NOT need to memorize these. The following is just a sample of array methods available to you. You'll come to be more familiar with these as you need them and look them up in documentation.

tl;dr: The more you Google them, the better you'll remember them.

Push/Pop

These Javascript methods also exist in Ruby and are used the same way.

numbers = [1, 2, 3, 4, 5]
# => [1, 2, 3, 4, 5]

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

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

numbers.pop
# => 9

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

Sort

Organizes array values from lowest to highest. Numbers and strings. Compare this to how Javascript handles sort()

numbers = [3, 1, 5, 2, 4]
# => [3, 1, 5, 2, 4]

numbers.sort
# => [1, 2, 3, 4, 5]

Delete

• Removes an argument from an array. If there are multiple instances of that argument, it will delete them all
• Look up: .delete_at(), .slice()

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

numbers.delete(2)
# => 2

numbers
# => [3, 1, 4]

Symbols

Symbols are immutable, constant values. That means they contain the same value through the entirety of a program and cannot be changed.

• Kind of like a string that never changes
• Syntax: variable_name = :symbol_name
• No Javascript equivalent (until ES6 came along!))

favorite_animal = :dog
# => :dog

favorite_animal.upcase!
# NoMethodError: undefined method `upcase!' for :dog:Symbol
# Did you mean?  upcase

When/why would you use symbols?

• Most common use is as keys in hashes, the Ruby equivalent of objects (more on that later)
• Make sure values that need to be constant stay constant
• Enhance performance, use less memory

Every string you create is unique and takes up space on your computer, even if they're the same value! When we're busy looking up key/value pairs, we don't want to be wasting memory - we want it to be fast!

Let's watch:

"Your Name".object_id
#=> a number

"Your Name".object_id
#=> a different number

:your_name.object_id
#=> a number

:your_name.object_id
#=> the same number!

Hashes

A Ruby hash is an unordered, dictionary-like collection organized by key-value pairs.

A hash is very similar to a Javascript object.

Ahmad = { name: 'Ahmad', age: 0 }

Notice that is looks exactly like a JS object except the keys are symbols, not strings.

sei_class = {
  teacher: "Ahmad",  
  students: ["Tony", "Steve", "Bruce"],  
  classroom: 3,
  in_session: true,  
  schedule: {  
    morning: "Ruby Basics",
  }
}  
# => {:teacher=>"Ahmad", :students=>["Tony", "Steve", "Bruce"], :classroom=>3, :in_session=>true, :schedule=>{:morning=>"Ruby Basics"}}

Accessing hash values...

sei_class[:teacher]
# => "Ahmad"

Modifying hash values...

sei_class[:teacher] = "Ebere"
# => "Ebere"

You can also use strings as hash keys...

sei_class = {
  "teacher" => "Ahmad",  
  "students" => ["Tony", "Steve", "Bruce"],  
  "classroom" => 3,  
  "in_session" => true,  
  "schedule" => {  
    "morning" => "Ruby Basics",
    "afternoon" => "FEWD"
  }
}  

Then can access in this way...

sei_class["teacher"]
# => "Ahmad"

And modify...

sei_class["teacher"] = "Ebere"
# => "Ebere"

Note the use of => (or "hash rockets") instead of : when using strings as keys.

Hash Methods

Like arrays, Ruby also provides us with a library of hash methods.

• Again, the Ruby documentation is a great resource.
• As mentioned with arrays, do not worry about memorizing these methods. Just know how to look them up should the need arise.

Keys

Returns an array with all the keys in a hash.

sei_class.keys
# => [:teacher, :students, :classroom, :in_session, :schedule]

Merge

Combines two hashes. If both of your hashes have the same key, the one in the hash you set as the argument in the parameters will take precedence.

classroom = {
 room: 1  
}  
# => {:room=>1}

locations = {
 location_one: "Gotham",  
 location_two: "NY",  
 location_three: "Jeddah"  
}  
# => {:location_one=>"Gotham", :location_two=>"NY", :location_three=>"Jeddah"}

silly_hash = classroom.merge(locations)
# => {:room=>1, :location_one=>"Gotham", :location_two=>"NY", :location_three=>"Jeddah"}

classroom
# => {:room=>1}

locations
# => {:location_one=>"Gotham", :location_two=>"NY", :location_three=>"Jeddah"}

silly_hash
# => {:room=>1, :location_one=>"Gotham", :location_two=>"NY", :location_three=>"Jeddah"}

Ranges

Use ranges to quickly generate arrays of data types.

Parentheses Min and max value, separated by two periods. Generate array using .to_a method

(1..5).to_a
# => [1, 2, 3, 4, 5]

("a".."z").to_a
# => ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]

Normally, only two dots are used. If a third dot is used, the last value in the range is excluded.

(0...5) represents the numbers 0 through 4.

Lab: Data Collection Exercise

Complete the exercises in this document.

Blocks

Any code surrounded by curly braces is a block.

2.times {
  print "Hey!"
}

With blocks, you can group a set of instructions together so that they can be passed around your program.

The curly braces can also be traded for the words do and end, which is nice if your block is longer than one line.

loop do
  print "Hey!"
end

Loops

One of the most common things we do as developers is to iterate through data structures.

Whenever we talk about data in Ruby, its important to review how Ruby handles groups of data.

We learned how to iterate over collections in Javascript using loops. Now we're going to learn the same in Ruby.

Review JS Loops

What loops did we use in Javascript?

while, do...while, for, for...in, .forEach

Looping with Ruby

In JS if we wanted to print numbers 0 through 3 we would:

for(var i = 0; i < 3; i++) {
  console.log(i);
}
// > 0
// > 1
// > 2

In Ruby this is much cleaner:

3.times { |i| puts i }
# > 0
# > 1
# > 2

names = ["Ebere","Yassir","Ahmad", "Atheer", "Mike", "Sami" , "Alanoud" ]
names.length.times{ |i| puts "hello #{i} = #{names[i]}"}

times is a method that takes a block. A block is just a chunk of code that may or may not take arguments. The closest thing to a block in ES6-land would be an (anonymous) arrow function.

We also have .upto and .downto methods for looping.

Yes there are for loops in Ruby but we DO NOT use them

But, the closest equivalent to Javascript's for loop is Rubys for...in loop

users = ["Blossom", "Bubbles", "Buttercup"]
for user in users do
  puts user
end

We can also iterate over arrays:

arr = [10, 20, 30]

arr.each { |num| puts num }
# > 10
# > 20
# > 30

arr.map { |num| num / 10 }
# => [1, 2, 3]

each and map also take blocks (just like forEach and map take callbacks in JS).

What is the difference between map & each?

Each is like a more primitive version of map…

It gives you every element so you can work with it, but it doesn’t collect the results. Each always returns the original, unchanged object. While map does the same thing, but… It returns a new array with the transformed elements.

For blocks with longer lines or multiple lines, replace { and } with do and end

arr.map do |num|
  "#{num / 10} is great!"
end
# => ["1 is great!", "2 is great!", "3 is great!"]

And we can iterate over hashes:

hash = { a: 1, b: 2, c: 3 }
hash.each do |key, val|
  puts "the value of #{key} is #{val}"
end
# > the value of a is 1
# > the value of b is 2
# > the value of c is 3

Exercise: Other types of Loops in Ruby (30 minutes)

while

input = ""
puts "You must guess the Magic Words to exit the while loop!"
while input != "Magic Words" do
  puts "What are the Magic Words?"
  input = gets.chomp
end
puts "You made it out! Congrats!"

until

input = ""
puts "You must guess the Magic Words to exit the while loop!"
until input == "Magic Words" do
  puts "What are the Magic Words?"
  input = gets.chomp
end
puts "You made it out! Congrats!"

loop

puts "You must guess the Magic Words to exit the while loop!"
loop do
  puts "What are the Magic Words?"
  input = gets.chomp
  break if input == "Magic Words"
end
puts "You made it out! Congrats!"

.times

users = ["Blossom", "Bubbles", "Buttercup"]
users.length.times do |index|
  puts users[index]  
end

Further Reading on Ruby loops

Exercise: Practice Each (15 minutes)

Use each to do the following...

• Say hello to everybody in the below array of names (sample output: Hello Donald!).

  names = [ "Donald", "Daisy", "Huey", "Duey", "Luey" ]

• Print out the squared values of every number in this numbers array.

  numbers = [ 1, 3, 9, 11, 100 ]

• Print out the Celsius values for an array containing Fahrenheit values.

  Hint: C = (F - 32) * (5 / 9)

  fahrenheit_temps = [ -128.6, 0, 32, 140, 212 ]

• Insert all the values in the artists array into the ninja_turtles array.

  artists = [ "Leonardo", "Donatello", "Raphael", "Michelangelo" ]
  ninja_turtles = []

• Bonus: Print out every possible combination of the below ice cream flavors and toppings.

  flavors = [ "vanilla", "chocolate", "strawberry", "butter pecan", "cookies and cream", "rainbow" ]
  toppings = [ "gummi bears", "hot fudge", "butterscotch", "rainbow sprinkles", "chocolate sprinkles" ]

Hint

Use nested enumerable methods or check out product.

Map (30 minutes)

Explore 1

Run these two snippets separately:

cart = ["shoes", "watch", "computer"]
uppercase = cart.each do |product|
  caps_product = product.upcase
  puts caps_product
  caps_product
end
puts uppercase.join(", ")

cart = ["shoes", "watch", "computer"]
uppercase = cart.map do |product|
  caps_product = product.upcase
  puts caps_product
  caps_product
end
puts uppercase.join(", ")

How would you explain the difference in the result?

• .each executes the code block for each item in the original array and returns the original array regardless of what the block returns.
• .map returns a new array with the changes in the block applied to each element.

Explore 2

Consider:

cart = ["shoes", "watch", "computer"]
uppercase = []
cart.each{|product| uppercase.push(product.upcase) }
puts uppercase.join(", ")

cart = ["shoes", "watch", "computer"]
uppercase = cart.map{|product| product.upcase }
puts uppercase.join(", ")

What is the difference in the result of these two snippets?

Nothing: they have the same result. They are two ways of doing the same thing.

Explore 3: Bang

Consider:

cart = ["shoes", "watch", "computer"]
uppercase = cart.map{|product| product.upcase }
puts cart
puts uppercase

Below is the same snippet, but with .map! instead of .map.

What does ! often indicate in Ruby?

That this method is "dangerous", usually because it will modify, or mutate the object upon which it was called.

cart = ["shoes", "watch", "computer"]
uppercase = cart.map!{|product| product.upcase }
puts cart
puts uppercase

What's the difference between .map and .map!?

.map leaves the original array alone, whereas .map! changes it.

Exercise: Practice Map (15 minutes)

Use map to do the following...

1. Create an array that appends "Duck" to everybody in this array of first names

first_names = [ "Donald", "Daisy", "Daffy" ]

#= ["Donald Duck", "Daisy Duck", "Daffy Duck"]

2. Create an array containing the squared values of every number in this array.

numbers = [ 1, 3, 9, 11, 100 ]

# => [1, 9, 81, 121, 10000]

3. Create an array with the Celsius values for these Fahrenheit values.

Hint: C = (F - 32) * (5 / 9)

fahrenheit_temps = [ -128.6, 0, 32, 140, 212 ]

#=> [-89.2, -17.8, 0, 60, 100]

Methods

As stated before, everything in Ruby is an object so there is no distinction in this language between functions and methods. Under the hood, even seemingly stand-alone functions are in fact associated with an object. The convention, however, is to call these methods.

We use the word method in Ruby, never function. If we do it's mostly out of habit.

A method is made up of a few components. Take a look at the following method.

def double( number )
   doubled_number = number * 2
   return doubled_number
end  

double( 3 )
# => 6

double 3
# => 6

This method has several components to point out:

• def - the Ruby equivalent of function
• double - the method name in the below example
• number - the argument name in the below example
• end - closes the method

Passing arguments in Ruby works fairly similar to how it does in JS. They get passed as comma separated values after the method name.

def hello(name, greeting, small_talk, punctuation)
  "#{greeting} #{name}, #{small_talk}#{punctuation}"
end

Lets think back to the behaviors of arguments in JS. Remember how lenient it is?

In Ruby, if you specify a number of arguments, the function must take that number of arguments. No more, No less.

Less

$ hello("Jamie", "Hark", "frickin' cold eh")

=> ArgumentError: wrong number of arguments (given 3, expected 4)

More

$ hello("Jamie", "Hark", "frickin' cold eh", ".", "Forsooth, ye yonder pilgrim is quite the bespoke son of a tailors daughter, ai?")

=> ArgumentError: wrong number of arguments (given 5, expected 4)

SIDENOTE: Ruby's errors are amazing. Use them!

There are some fun ways to play with arguments and define further behavior:

Default arguments

def drink_milk(thirsty = true)
  return "I'm not thirsty" unless thirsty

  "mmmmmm... milk...."
end

Woah, that return statement?

In Ruby, returns are implicit by design. Ruby will always assume that the last line of the method will be returned. So why the first return?

Can you read it in English? One of Ruby's biggest benefitsis that it reads pretty closely to English

Additionally, you can add the statements if and unless to your return statement, which acts similarly to an if block.

function apiCall(err, data){
  if (err){
    return err;
  } 
  //Do stuff
}

vs.

def api_call(err, data)
  return err if err
  #Do Stuff
end

Everything is an Expression

def add(a, b)
  a + b
end

add(1, 2) # => 3

add(1, 2, 3)
# > ArgumentError: wrong number of arguments (given 3, expected 2)

Notice we do not need the keyword return. The last line hit by the method will always be the return value. This is called an implicit return.

Predicate Methods (?)

This is similar to adding the bang to the end of a method. Predicate methods using ? returns a boolean value.

  5.odd?
  # true
  5.even?
  # false
  something = "A thing"
  # => "A thing"
  something.nil?
  # => false

Ruby Code Style Guide

The Ruby community is very opinionated about styling. As you are starting out, you MUST follow these rules.

Here are the most important rules

Casing

• All variables and methods must use snake_case
• All classes and modules must use CamelCase
• All constants (besides classes and modules) must use SCREAMING_SNAKE_CASE

Blocks

• A single line block must use { and }
• A multi-line must use do and end
• If an argument is unused it should start with _ (or just be named _)
  • hash.each { |_key, val| puts val }

Methods

• A method should end with a ? if an only if it always returns a boolean
  • These are called predicate methods
• A method ending in ! should be a dangerous version of the method sans !
  • dangerous means either that it can mutate the object or that can raise an error
• Don't name methods like get_foo, set_foo. They should be foo and foo=
• Do use attr_reader and attr_writer
• Do not use parens when calling a method without args
  • super is one possible exception
• Do use parens for every method except for DSLs (and a small list of other common methods)
  • attr_reader, puts, require, include, it, has_many, ...