[英]Scala Future and Either Transformation
I have a variable of type我有一个类型的变量
val input: Future[Seq[Either[ErrorClass, Seq[WidgetCampaign]]]] = ???
I want to traverse this input and remove all duplicates WidgetCampaign
and return the output as我想遍历这个输入并删除所有重复的
WidgetCampaign
并将 output 返回为
val result: Future[Either[ErrorClass,Set[WidgetCampaign]]] = ???
How can I achieve this?我怎样才能做到这一点?
Firstly, the processing can all be done inside the Future
using a map
call:首先,可以使用
map
调用在Future
内部完成所有处理:
input.map(process)
So the problem is to write a process
function that converts between Seq[Either[ErrorClass, Seq[WidgetCampaign]]
and Either[ErrorClass, Set[WidgetCampaign]]
.所以问题是编写一个在
Seq[Either[ErrorClass, Seq[WidgetCampaign]]
和Either[ErrorClass, Set[WidgetCampaign]]
之间转换的process
function 。
Start by making a couple of type aliases to make the rest of the code cleaner.首先制作几个类型别名以使代码更清晰的 rest。
type InType = Either[ErrorClass, Seq[WidgetCampaign]]
type OutType = Either[ErrorClass, Set[WidgetCampaign]]
The process itself can be done with an awkward flatMap
call, but a simple recursive function is probably best:这个过程本身可以通过一个尴尬的
flatMap
调用来完成,但是一个简单的递归 function 可能是最好的:
def process(input: Seq[InType]): OutType = {
@annotation.tailrec
def loop(rem: List[InType], res: Set[WidgetCampaign]): OutType =
rem match {
case Nil => // Stop when no more elements to process
Right(res)
case Left(e) :: _ => // Stop on first error
Left(e)
case Right(s) :: tail => // Add this Seq to the result and loop
loop(tail, res ++ s)
}
loop(input.toList, Set.empty[WidgetCampaign])
}
This is a standard pattern for recursive logic where the recursive function itself is wrapped in an outer function.这是递归逻辑的标准模式,其中递归 function 本身被包裹在外部 function 中。 The inner function is then tail-recursive for efficiency, with the intermediate result being passed down through the recursive call.
然后内部 function 为提高效率而进行尾递归,中间结果通过递归调用向下传递。
The input is converted to a List
to make pattern matching easier.输入被转换为
List
以使模式匹配更容易。
This is untested, but it compiles so that's a start...这是未经测试的,但它可以编译,所以这是一个开始......
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