理解 yield map

Question

我尝试使用 for comprehension 将字符串映射到 MyData 大小写 class。

以下是我尝试失败的方法：

case class MyDataProperty(name: String, value: String)
case class MyData(props: List[MyDataProperty])


def makeMyData(configs: List[Config]): Map[String, MyData] = {
    for {
      // loop through all configurations
      conf <- configs
      // Retrieve each config's list of properties and make a list of MyDataProperty object from it
      props <- for(prop <- conf.properties) yield (MyDataProperty(prop.name, prop.value))
    } yield (conf.name -> MyData(props)) toMap
}

这段代码给我多个编译错误。这种理解窝和出图的正确搭建方法是什么？

Answer 1

使用 for comprehensions 您的代码应如下所示：

def makeMyData(configs: List[Config]): Map[String, MyData] =
  (for {
    conf <- configs
    props = for (prop <- conf.properties) yield MyDataProperty(prop.name, prop.value)
  } yield conf.name -> MyData(props)).toMap

理解 yield map

for comprehension to yield map

scala

for-comprehension