如何将 Seq[Try] 转换为 Try[Seq] [英] How to transform a Seq[Try] to a Try[Seq]

问题描述

使用Futures，有一种简单的方法可以将Seq[Future] 转换为Future[Seq]:

Future.sequence(seqOfFutures)

我用 Try 找不到类似的东西.

它适用于 foldLeft，但我真正喜欢的是 Try.sequence(seqOfTry).

不提供这样的功能是不是有原因?

这是如何正确完成的?

语义:

成功值列表:Success(Seq(1,2,3,4))

对于失败有两种可能:

• 第一次失败 Failure 并返回它.这是由这个问题处理的:listtryt-to-trylistt-in-scala>

• 收集所有 Failure 并返回复合"失败.

对于'复合'失败还有解决方案吗?

解决方案

根据 Luis 的建议 Validated 专为错误累积而设计，因此请考虑 traverse 像这样

la.traverse(_.toEither.toValidatedNec)lb.traverse(_.toEither.toValidatedNec)

哪个输出

res2:cats.data.ValidatedNec[Throwable,List[Int]] = Invalid(Chain(java.lang.RuntimeException:boom, java.lang.RuntimeException: crash))res3:cats.data.ValidatedNec[Throwable,List[Int]] = Valid(List(1, 2, 3))

哪里

importcats.syntax.traverse._导入cats.instances.list._导入cats.syntax.either._导入 scala.util.{失败，成功，尝试}val la: List[Try[Int]] = List(Success(1), Success(2), Failure(new RuntimeException("boom")), Success(3), Failure(new RuntimeException("crash")))val lb: List[Try[Int]] = List(Success(1), Success(2), Success(3))

<小时>

没有错误累积，我们可以像这样排序

导入cats.implicits._序列

哪个输出

res0: scala.util.Try[List[Int]] = Failure(java.lang.RuntimeException:boom)

With Futures there is an easy way to transform Seq[Future] to a Future[Seq]:

Future.sequence(seqOfFutures)

I could not find an analog thing with Try.

It works with foldLeft but what I really like would have something like Try.sequence(seqOfTry).

Is there a reason that such a function is not provided?

How is this done properly?

Semantics:

A List of the values on Success: Success(Seq(1,2,3,4))

For Failure there are 2 possibilities:

• Fails on the fist Failure and returns it. This is handled by this question: listtryt-to-trylistt-in-scala

• Gathers all Failures and returns a 'compound' Failure.

Is there also a solution for the 'compound' Failure?

解决方案

As per Luis' suggestion Validated is designed for error accumulation so consider traverse like so

la.traverse(_.toEither.toValidatedNec)
lb.traverse(_.toEither.toValidatedNec)

which outputs

res2: cats.data.ValidatedNec[Throwable,List[Int]] = Invalid(Chain(java.lang.RuntimeException: boom, java.lang.RuntimeException: crash))
res3: cats.data.ValidatedNec[Throwable,List[Int]] = Valid(List(1, 2, 3))

where

import cats.syntax.traverse._
import cats.instances.list._
import cats.syntax.either._
import scala.util.{Failure, Success, Try}

val la: List[Try[Int]] = List(Success(1), Success(2), Failure(new RuntimeException("boom")), Success(3), Failure(new RuntimeException("crash")))
val lb: List[Try[Int]] = List(Success(1), Success(2), Success(3))

---

Without error accumulation we could just sequence like so

import cats.implicits._
la.sequence 

which outputs

res0: scala.util.Try[List[Int]] = Failure(java.lang.RuntimeException: boom)

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