Type inference in ZIO giving Any in for comprehension-CodePudding

So I have written a method to count the number of lines in a file in ZIO.

def lines(file: String): Task[Long] = {
    def countLines(reader: BufferedReader): Task[Long] = Task.effect(reader.lines().count())
    def releaseReader(reader: BufferedReader): UIO[Unit] = Task.effectTotal(reader.close())
    def acquireReader(file: String): Task[BufferedReader] = Task.effect(new BufferedReader(new FileReader(file), 2048))

    Task.bracket(acquireReader(file), releaseReader, countLines)
  }

Now inside my run method when I try to extract the result like this:

for {
      lines <- linesV3("src/main/scala/FileIO.scala") //Type of lines showing as Any
      _ <- putStrLn(lines.toString) //This line throws error as it cannot convert Any to String
    }

The type of lines is coming as Any instead of Long. Why is this so? If I use flatMap then the type is inferred correctly.

CodePudding user response：

There's no problem with the code you posted here. The issue must be arising from somewhere else in your program. Maybe you are missing the yield after the for comprehension. I don't know if that is a copying error.

CodePudding user response：

so the solution was fairly similar. As soon as I add a yield after the for comprehension the type inference starts working correctly

for {
  lines <- linesV3("src/main/scala/FileIO.scala")
  _ <- putStrLn(lines.toString)
} yield ()

The toString method is required because putStrLn accepts only String parameters.