為什么覆寫引導程式，不適用于運行方法？

我正在學習 ZIO 2.x，Runtime使用bootstrap層配置時，它不起作用。

object RuntimeCustom extends ZIOAppDefault {

  // It's not work, And I don't know why?
  override val bootstrap = EmailService.live
  
  def run = (for {
    _ <- ZIO.debug("Start...")
    _ <- EmailService.send("God", "Hi")
    _ <- ZIO.debug("End...")
  } yield ())
}

得到一個錯誤：

[error] /Users/changzhi/github-repo/zio-start/src/main/scala/zio/reference/experiment/core/RuntimeCustom.scala:35:7: 
[error] 
[error] ──── ZIO APP ERROR ───────────────────────────────────────────────────
[error] 
[error]  Your effect requires a service that is not in the environment.
[error]  Please provide a layer for the following type:
[error] 
[error]    1. example.EmailService
[error] 
[error]  Call your effect's provide method with the layers you need.
[error]  You can read more about layers and providing services here:
[error]  
[error]    https://zio.dev/next/datatypes/contextual/
[error] 
[error] ──────────────────────────────────────────────────────────────────────
[error] 
[error]     _ <- EmailService.send("God", "Hi")
[error]       ^
[error] one error found
[error] (Compile / compileIncremental) Compilation failed

如果我用 替換provide，它可以作業。

object RuntimeCustom extends ZIOAppDefault {
  
  def run = (for {
    _ <- ZIO.debug("Start...")
    _ <- EmailService.send("God", "Hi")
    _ <- ZIO.debug("End...")
  } yield ())
    // This can works, have no doubt
    .provide(EmailService.live)
}

完整版程式在這里

package example

import zio._
trait EmailService {
  def send(user: String, content: String): Task[Unit]
}
object EmailService {
  def send(user: String, content: String): ZIO[EmailService, Throwable, Unit] =
    ZIO.serviceWithZIO[EmailService](_.send(user, content))

  val live: ZLayer[Any, Nothing, EmailService] = 
    ZLayer.fromZIO( ZIO.succeed(EmailServiceFake()) <* Console.printLine("Init EmailService") ).orDie
}

case class EmailServiceFake() extends EmailService {
  override def send(user: String, content: String): Task[Unit] =
    Console.printLine(s"sending email to $user")
}

object RuntimeCustom extends ZIOAppDefault {

  
  // It's not work, And I don't know why?
  //override val bootstrap = EmailService.live
  
  def run = (for {
    _ <- ZIO.debug("Start...")
    _ <- EmailService.send("God", "Hi")
    _ <- ZIO.debug("End...")
  } yield ())
    // This can works, have no doubt
    .provide(EmailService.live)
}

uj5u.com熱心網友回復：

ZIOAppDefault適用于不需要額外服務的應用程式，假設它們只會“需要”內置服務，因為您已經使用該方法提供了其他要求。provide

如果您想使用該bootstrap方法，您應該擴展ZIOApp并覆寫environmentTagandEnvironment欄位，以便該run機制知道如何構造最終環境。

import zio._

object App extends ZIOApp {
  
  // Tell ZIO how the environment is constructed
  override val environmentTag: EnvironmentTag[Environment] = EnvironmentTag[Environment]
  
  // Tell the app which layers will be leftover from the `run`
  override type Environment = FooService
  
  // The app how to construct those remaining layers
  override val bootstrap = FooService.layer
  
  
  val run = FooService.doFoo
  
  
}

class FooService {
  def doFoo: UIO[Unit] = ZIO.unit
}

object FooService {
  val layer = ZLayer.succeed(new FooService)
  
  def doFoo = ZIO.serviceWithZIO[FooService](_.doFoo)
}

編輯

使用原始示例來證明這是有效的：

import zio._


trait EmailService {
  def send(user: String, content: String): Task[Unit]
}
object EmailService {
  def send(user: String, content: String): ZIO[EmailService, Throwable, Unit] =
    ZIO.serviceWithZIO[EmailService](_.send(user, content))

  val live: ZLayer[Any, Nothing, EmailService] = 
    ZLayer.fromZIO( ZIO.succeed(EmailServiceFake()) <* Console.printLine("Init EmailService") ).orDie
}

case class EmailServiceFake() extends EmailService {
  override def send(user: String, content: String): Task[Unit] =
    Console.printLine(s"sending email to $user")
}

object RuntimeCustom extends ZIOApp {

  
  // It's not work, And I don't know why?
  override val bootstrap = EmailService.live 
  
  override type Environment = EmailService
  
  override val environmentTag: EnvironmentTag[Environment] = EnvironmentTag[Environment]
  
  
  def run = (for {
    _ <- ZIO.debug("Start...")
    _ <- EmailService.send("God", "Hi")
    _ <- ZIO.debug("End...")
  } yield ())
}

https://scastie.scala-lang.org/02MMaWS2S6Wwe55a24H7Sg

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