(可选)将项目添加到Scala地图 [英] Optionally adding items to a Scala Map

问题描述

我正在寻找解决该问题的惯用方法.

I am looking for an idiomatic solution to this problem.

我正在构建val Scala(不可变)地图，并想选择添加一个或多个项目:

I am building a val Scala (immutable) Map and would like to optionally add one or more items:

val aMap =
  Map(key1 -> value1,
      key2 -> value2,
      (if (condition) (key3 -> value3) else ???))

如何在不使用var的情况下完成此操作?用什么代替????使用+运算符更好吗?

How can this be done without using a var? What should replace the ???? Is it better to use the + operator?

val aMap =
  Map(key1 -> value1,
      key2 -> value2) +
  (if (condition) (key3 -> value3) else ???))

一种可能的解决方案是:

One possible solution is:

val aMap =
  Map(key1 -> value1,
      key2 -> value2,
      (if (condition) (key3 -> value3) else (null, null))).filter {
        case (k, v) => k != null && v != null
      }

这是最好的方法吗?

推荐答案

类似的事情

val optional = if(condition) Seq((key3 -> value3)) else Nil
val entities = Seq(key1 -> value1, key2 -> value2) ++ optional
val aMap = Map(entities:_*)

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