Type EnvT can not be found

Question

I have the following code that does not compiled:

trait DbSetup[F[_]] {

  type EnvT[A] = OptionT[F, A]

  def system: EnvT[Env]

  def user: EnvT[String]

  def password: EnvT[String]

  def address: EnvT[String]

}

object DbSetup {

  def read[F[_]: Monad](s: DbSetup[F]): EnvT[Configuration] = ???

}

the compiler complains:

not found: type EnvT
[error]   def read[F[_]: Monad](s: DbSetup[F]): EnvT[Configuration] = ???
[error]                                         ^
[error] one error found
[error] (Compile / compileIncremental) Compilation failed

How to import the type EnvT into the object scope?

@user well, we can't be sure. OP didn't provide enough information. But that's an option. — Dmytro Mitin, Jun 05 '20 at 20:34
https://stackoverflow.com/questions/59662424/scala-methods-in-trait-cant-use-methods-from-companion-object/ — Dmytro Mitin, Jun 05 '20 at 20:36

score 4 · Accepted Answer · answered Jun 05 '20 at 20:30

4

Try

def read[F[_]: Monad](s: DbSetup[F]): s.EnvT[Configuration] = ???

answered Jun 05 '20 at 20:30

Dmytro Mitin

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3

@zero_coding Google for "path-dependent type", "method dependent type" https://stackoverflow.com/questions/54879353/how-to-write-method-with-dependent-type-in-scala Have you looked at the link I gave https://stackoverflow.com/questions/54879353/how-to-write-method-with-dependent-type-in-scala ? – Dmytro Mitin Jun 05 '20 at 20:40
2

@zero_coding Every instance of `DbSetup` kinda has its own version of `EnvT`. By doing `s.EnvT`, you're accessing `s`'s specific copy of that type – user Jun 05 '20 at 20:40
@zero_coding Could you be more specific what confuses you? – Dmytro Mitin Jun 05 '20 at 20:41
1

@zero_coding https://stackoverflow.com/questions/2693067/what-is-meant-by-scalas-path-dependent-types – Dmytro Mitin Jun 05 '20 at 20:43
I was confused, how do you know that can be written `s.EnvT[Configuration]` – softshipper Jun 05 '20 at 20:46
3

@zero_coding well, I couldn't know that it was specifically `s.EnvT`. It could be any `x.EnvT` for `x: DbSetup[F]`. For example for `val x = new DbSetup[F] { override ...}`. You could make `import x._` so that you could access `x.EnvT` as just `EnvT`. But there was already `x: DbSetup[F]` in the scope, namely `s`. – Dmytro Mitin Jun 05 '20 at 20:54

Type EnvT can not be found

1 Answers1