ruby_metaprogramming_example_engibeering.rb

class Person
  attr_reader :full_name, :age, :profession, :favorite_food

  def initialize(full_name, age, profession, favorite_food)
    @full_name = full_name
    @age = age
    @profession = profession
    @favorite_food = favorite_food
  end
end

class People
  attr_reader :people, :attributes

  def initialize(people)
    @people = people
    @attributes = define_attributes

    define_dynamic_finders
  end

  private

  def define_attributes
    people.map do |person|
      person.instance_variables.map(&:to_s).map do |attribute|
        attribute.gsub("@", "")
      end
    end.flatten.uniq
  end

  def define_dynamic_finders
    attributes.each do |attribute|
      self.class.class_eval do
        define_method("find_by_#{attribute}") do |argument|
          people.select { |person| person.send(attribute) == argument }
        end
      end
    end
  end
end

group = People.new([
  Person.new("Bryan Woods", 27, :programmer, "sushi"),
  Person.new("Kurt Cobain", 27, :musician, "apple pie"),
  Person.new("Shawn Carter", 43, :musician, "pizza"),
  Person.new("Jonathan Franzen", 53, :author, "macaroni and cheese")
])

musicians = group.find_by_profession(:musician)
musicians.each { |musician| puts "#{musician.full_name} is a musician!" }

twenty_seven_year_olds = group.find_by_age(27)
twenty_seven_year_olds.each do |person|
  puts "#{person.full_name} is #{person.age} and loves #{person.favorite_food}!"
end