Ruby syntax 101

osx.sh

xcode-select --install
brew update
brew install git

git clone https://github.com/sstephenson/rbenv.git ~/.rbenv
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bash_profile
echo 'eval "$(rbenv init -)"' >> ~/.bash_profile
git clone https://github.com/sstephenson/rbenv-gem-rehash.git ~/.rbenv/plugins/rbenv-gem-rehash
git clone https://github.com/sstephenson/ruby-build.git ~/.rbenv/plugins/ruby-build
source ~/.bash_profile

rbenv install 2.6.8
rbenv global 2.6.8

ruby.rb

# Everything after the '#' character is a comment
# Run these lines in an interactive ruby interpreter (irb) to "feel" them

9/2 == 4
9/2.0 == 4.5 # Same as 9.0/2 or 9.0/2.0 or 9.to_f/2

2**8 == 256

[1, 2] + [2, 3] == [1, 2, 2, 3]
[1, 2] - [2, 3] == [1]
[1, 2] | [2, 3] == [1, 2, 3]
[1, 2] & [2, 3] == [2]

a = []
a << "toto"
a == ["toto"]

10.times do |n|
  puts n
end

10.times { |n| puts n } # oneliner syntax

1.upto(10) do |n|
  puts n
end

[1, 2, 3].each do |i|
  puts i
end

(1..10).each do |n|
  puts n
end

condition1 = ""
condition2 = false
if condition1
  puts "condition1 is not false nor nil"
elsif condition2
  puts "condition1 is false or nil, and condition2 isn't"
else
  puts "condition1 and condition2 are both false or nil"
end

# Only strongly-typed 'false' and 'nil' (ruby null equivalent) will be rejected by 'if'
# Eg. 0 et "" are equivalent to true

{ first_name: "Julien" } == { :first_name => "Julien" } 
{ first_name: "Julien" } != { "first_name" => "Julien" }

# :first_name is a symbole. It's a kind of constant string used as a software internal key.

my_variable = :first_name
my_hash = { first_name: "Julien" }

# These all return "Julien" 
my_hash[my_variable]
my_hash[:first_name]
{ first_name: "Julien" }[:first_name]

my_hash.each{ |key, value| puts value }

def my_function
  42
end

my_function == 42

# return isn't a mandatory keyword in a function. Then last line of a function will be returned.

def my_function(i)
  i * 2
end

my_function(10) == 20

# These all return the same
[1, 2, 3].map{ |i| i * 2 }
["1", "2", "3"].map(&:to_i).map{ |i| i * 2 }
[2, 4, 6]

def my_function(i: 7)
  i * 2
end
my_function(i: 10) == 20
my_function == my_function() # 14

def my_function(i:)
  i * 2
end
my_function(i: 10) == 20
my_function # ArgumentError (missing keyword: i)

class User
  def initialize(name)
    @name = name
  end

  def greet
    puts "Bonjour #{@name}"
  end
end

user = User.new("Julien")
user.greet == "Bonjour Julien"
user.name # NoMethodError (undefined method `name' for User instance)

class User
  def initialize(name)
    @name = name
  end

  def name
    @name
  end
  
  def name=(value)
    @name = value
  end
end

user = User.new("Julien")
user.name == "Julien"
user.name = "Another name"
user.name == "Another name"

class User
  attr_reader :name

  def initialize(name)
    @name = name
  end
end

user = User.new("Julien")
user.name == "Julien"
user.name = "Another name" # NoMethodError (undefined method `name=' for User instance)

class User
  attr_accessor :name

  def initialize(name)
    @name = name
  end
end

# @ are instance variables.
# Note: in Rails, @variables in controllers have a special meaning

ubuntu.sh

sudo apt-get update
sudo apt-get install build-essential libffi-dev libssl-dev libreadline-dev zlib1g-dev git

git clone https://github.com/sstephenson/rbenv.git ~/.rbenv
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
echo 'eval "$(rbenv init -)"' >> ~/.bashrc
git clone https://github.com/sstephenson/rbenv-gem-rehash.git ~/.rbenv/plugins/rbenv-gem-rehash
git clone https://github.com/sstephenson/ruby-build.git ~/.rbenv/plugins/ruby-build
source ~/.bashrc

rbenv install 2.6.8
rbenv global 2.6.8