adding_money.rb

require 'money'

class Apples
  def initialize(count)
    @count = count
  end

  def zero?
    @count.zero?
  end

  def to_s
    "#{@count} Apples"
  end
end

some_money = Money.new(100_00, "USD")
no_apples = Apples.new(0)
some_apples = Apples.new(3)

puts "$#{some_money} + #{no_apples}"
puts "= $#{some_money + no_apples}"
puts "$#{some_money} + #{some_apples}"
puts "= $#{some_money + some_apples}"

Output (click to reveal)

$100.00 + 0 Apples
= $100.00
$100.00 + 3 Apples
~/.gem/ruby/2.3.2/gems/money-6.7.1/lib/money/money/arithmetic.rb:112:in `+': TypeError (TypeError)