ruby_singleton_classes.rb

# frozen_string_literal: true

class Human
  # What does this mean? Who is owner of this instance variable?
  @created_humans = []

  @@humans_count = 0
  # What does mean this instruction
  class << self
    attr_accessor :created_humans
  end

  # And this?
  def self.humans_count
    @@humans_count
  end

  def self.to_s
    'Class Human'
  end

  attr_reader :name, :age

  def initialize(name:, age:)
    @name = name
    @age = age
    self.class.created_humans << self
    @@humans_count += 1
  end

  def to_s
    "#{name} -> #{age}"
  end
end

john = Human.new(name: 'John', age: 20)
max = Human.new(name: 'Max', age: 15)
barbara = Human.new(name: 'Barbara', age: 40)

# What about this
def john.to_s
  "I'm John, and I'm #{age} years old"
end

puts john
puts max
puts barbara
puts Human
puts Human.humans_count
puts Human.created_humans