double_splat.rb

class ChargeCustomer
  def charge!(customer:, amount:, note:)
    # do something
  end
end

class ChargeParams
  def initialize(order)
    @order = order
  end
  
  def to_hash # this is the magic of double-splat
    {
      customer: @order.customer,
        amount: @order.total,
          note: "Purchased #{@order.product.description}",
    }
  end
end


order         = Order.find(order_id)
charge_params = ChargeParams.new(order)

charge_customer = ChargeCustomer.new
charge_customer.charge!(**charge_params)
#                       ^^
#                       ||
#                       calls to_hash, then
#                       coerces to kwargs