gistfile1.rb

class Person
    PEOPLE = []
    
    attr_reader :name, :hobbies, :friends
    
    def initialize(name)
        @name = name
        @hobbies = []
        @friends = []
        PEOPLE << self
    end

    def has_hobby(hobby)
        @hobbies << hobby
    end
    
    def has_friend(friend)
        @friends << friend
    end

    def self.method_missing(m, *args)
        method = m.to_s
        if method.start_with?("all_with_")
            attr = method[9..-1]
            if self.public_method_defined?(attr)
                PEOPLE.find_all do |person|
                    person.send(attr).include?(args[0])
                end
            else
                raise ArgumentError, "Can't find #{attr}"
            end
        else
            super
        end
    end

end

j = Person.new("John")
p = Person.new("Paul")
g = Person.new("George")
r = Person.new("Ringo")
j.has_friend(p)
j.has_friend(g)
g.has_friend(p)
r.has_hobby("rings")

Person.all_with_friends(p).each do |person|
    puts "#{person.name} is friends with #{p.name}"
end

Person.all_with_hobbies("rings").each do |person|
    puts "#{person.name} is into rings"
end