   mutating func addOrder(_ order: Order) {
       orders.append(order)
   }
+
+    func dollarValue(btcPrice: Double) -> String {
+        return (bitcoinValue * btcPrice).dollars
+    }
 }
 
 enum BuySell: String {

      let o = orders.map({$0.summary(for: self)}).joined(separator: ", ")
      return "\(ticker): \(bitcoinValue.summary) BTC \(o)"
  }

  static func ticker(fromBitcoinMarketKey key: String) -> String? {
      guard key.hasPrefix("BTC_") else { return nil }

      let sorted = holdings.sorted(by: { $0.ticker < $1.ticker })
      let all: [String] = sorted.map({$0.description})
      let price = btcPrice != nil ? "BTC price: \(btcPrice!.dollars)\n" : ""
      return "\(price)\(all.joined(separator: "\n"))\n\(summary)"
  }
}
/*
