city.rb

lisbon = {
  # key     =>  value
  "country" => "Portugal", # string
  "population" => 2821876 # integer
}

# puts Lisbon.class
# uninitialized constant Lisbon (NameError)
# the program does not know a variable/constant named Paris
# (because we have not defined one)

puts lisbon.class
puts lisbon.size
# shares some methods with array
# both are enumerators

# CRUD
# students = ["paul", "john"]
# C: students << "george"
# R: students[1]
# U: students[1] = "ringo"
# D: students.delete_at(2) -> () because delete_at is a method


# Hash

# Create / Update
lisbon["monument"] = "Belém Tower"
#         key           value
p lisbon
# Read
puts lisbon["population"]
#               key
# Delete
lisbon.delete("population")
p lisbon

count.rb

students = {
  "paul" => 24,
  "mary" => 24,
  "mark" => 25
}

count_24 = students.count do |record| # grabs an array [key, value]
  name = record[0]
  age = record[1]
  age == 24
end

puts count_24

hash.rb

students =     [ "Peter", "Mary", "George", "Emma" ]
student_ages = [ 24     , 25    , 22      ,  20    ]
#                   0       1         2       3

students.each_with_index do |student, index|
  age = student_ages[index]
  puts "#{student} is at #{age} years old"
end

# Peter is 24 years old
# Mary is 25 years old
# [...]

hash_methods.rb

lisbon = {
  # key     =>  value
  "country" => "Portugal", # string
  "population" => 2821876, # integer
  "neighbourhoods" => ["Bairro Alto", "Alfama", "Mouraria"]
}

# Q: Is there a 'monument' key in the 'lisbon' hash?

key_present = false
lisbon.each do |key, _value|
  key_present = true if key == "monument"
end

puts key_present

puts lisbon.has_key?("population")
puts lisbon.has_value?("portugal") # => false 'portugal' != 'Portugal'
puts "====== Keys"
puts lisbon.keys
puts "====== Values"
puts lisbon.values

iterator.rb

lisbon = {
  # key     =>  value
  "country" => "Portugal", # string
  "population" => 2821876, # integer
  "neighbourhoods" => ["Bairro Alto", "Alfama", "Mouraria"]
}

# hash iteration
lisbon.each do |key, value|
  puts "The key is #{key} and the value is #{value}"
end
lisbon["neighbourhoods"].each do |neighbourhood|
  puts neighbourhood
end

# array iteration
students = ["paul", "john"]
students.each do |student|
  puts student
end

students.each_with_index do |student, index|
  puts "The students at index #{index} is #{student}"
end

method.rb

def tag(name, content, attrs = {})
  flat_attrs = attrs.map { |key, val| " #{key}='#{val}'" }.join
  "<#{name}#{flat_attrs}>#{content}</#{name}>"
end

puts tag('div', 'hello', {
  class: 'heading',
  id: 'main-heading',
  style: 'color: red;'
  })

recap.rb

# variable assignment
first_name = "Rui"
# putting the string "Rui" inside the 'box'/'container'

last_name = "Freitas"
# putting the string "Freitas" inside another 'box'/'container'

# defining a method
# it's like a recipe/instructions for a meal
def full_name(first_name, last_name) # arguments are like the ingredients
  "#{first_name} #{last_name}"
end

# now we are preparing/executing the meal
full_name(first_name, last_name)

# we can store the prepared meal/result for future use
my_name = full_name(first_name, last_name)

puts my_name

6 # Integer
3.14 # Float
"Hello, world!" # String
true # Boolean
['a', 'b', 'c', 'd'] # Array

cities = ["lisbon", "london"]
  #          0        1

puts cities[1]

symbols.rb

"country".object_id # => 70367016225180
"country".object_id # => 70367024806360

:country.object_id # => 2525468
:country.object_id # => 2525468