object_space.rb

# frozen_string_literal: true

module Finder
  attr_reader :id

  def initialize(**)
    @id = self.class.count
  end

  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods
    def find(id)
      scope.find { |car| car.id == id }
    end

    def all
      scope.to_a
    end

    def find_by(attribute, value)
      scope.find { |car| car.public_send(attribute) == value }
    end

    def method_missing(name, *arguments)
      if name.to_s =~ /^find_by_(.*?)$/
        find_by($1, arguments.first)
      else
        super
      end
    end

    def count
      scope.count
    end

    def scope
      ObjectSpace.each_object(self)
    end
  end
end

class Car
  include Finder

  def initialize(motor:)
    @motor = motor
    super
  end

  attr_reader :motor
end

first_car = Car.new(motor: "diesel")
second_car = Car.new(motor: "gazoline")
third_car = Car.new(motor: "electric")

p first_car.id
p second_car.id
p third_car.id

p Car.count
p Car.find(2)
p Car.all
p Car.find_by_motor("diesel")