我有一个不可变的数据结构,在其中我有嵌套在Map中的值,如下:
case class TradingDay(syms: Map[String, SymDay] = Map.empty)
case class SymDay(sym: String, traders: Map[String, TraderSymDay] = Map.empty)
case class TraderSymDay(trader: String, sym: String, trades: List[Trade] = Nil)
我有一份当天所有交易清单,我想生成TradingDay
结构,其中
case class Trade(sym: String, trader: String, qty: Int)
我正在尝试通过使用镜头(请参见附录)来更新这个结构,方法是通过我的交易进行折叠:
(TradingDay() /: trades) { (trd, d) =>
def sym = trd.sym
def trader = trd.trader
import TradingDay._
import SymDay._
import TraderSymDay._
val mod =
for {
_ <- (Syms member sym).mods(
_ orElse some(SymDay(sym)))
_ <- (Syms at sym andThen Traders member trader).mods(
_ orElse some(TraderSymDay(trader, sym)))
_ <- (Syms at sym andThen (Traders at trader) andThen Trades).mods(
trd :: _)
x <- init
} yield x
mod ! d
}
这个方法可行,但我在想是否有更简便的方式(例如只需添加一次到映射表中并修改映射表中键的值)。这似乎并没有比深拷贝更方便。
附录 - 镜头
object TradingDay {
val Syms = Lens[TradingDay, Map[String, SymDay]](_.syms, (d, s) => d.copy(syms = s))
}
object SymDay {
val Traders = Lens[SymDay, Map[String, TraderSymDay]](_.traders, (d, t) => d.copy(traders = t))
}
object TraderSymDay {
val Trades = Lens[TraderSymDay, List[Trade]](_.trades, (d, f) => d.copy(trades = f))
}