Implicit Not Visible in Scope

[Joe San]

In the following example., I was expecting something to be printed at line 1 and 2, but strangely I do not see that happening. My IDE complaints on line 3 that it is an unused import statement. Any ideas what is going wrong?

import scala.io.Source


class CSVReader[A] {
  def parse(path: String) = ReaderWithFile[A](path)

  case class ReaderWithFile[A](path: String) {
    def using(cfg: CSVParserConfig): Seq[A] = {
      val lines = Source.fromFile(path).getLines().mkString("\n")
      println(lines) // line 1
      println(cfg)   // line 2
      null
    }
  }
  object ReaderWithFile {
    implicit def parser2parsed[A](parser: ReaderWithFile[A]): Seq[A] = parser.using(defaultParserCfg)
  }
}
object CSVReader extends App {

  def parser[A] = new CSVReader[A]

  val myParser = parser

  import myParser.ReaderWithFile.parser2parsed // line 3, IDE says that this import is unused!

  myParser parse "csv-parser/test.csv" // expecting line 1 and 2 getting printed, but not!
  
  // but this works
  myParser parse "csv-parser/test.csv" using CSVParserConfig()

}

[Oliver Ruebenacker]

     Hello,

  Not sure why you expect lines 1 and 2 to be printed is method using is not called?

  Also, parser2parsed is not used.

     Best, Oliver

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Oliver Ruebenacker

Senior Software Engineer, Diabetes Portal, Broad Institute

[Joe San]

So the idea is if the user calls just this:

 myParser parse "csv-parser/test.csv"

I want the default to be applied!

[Oliver Ruebenacker]

  Not sure what you mean by "default"?

  Since myParser is of type CSVReader, it has a parse method that takes a String, so there is no reason for the compiler to look for an implicit conversion.

[Joe San]

So what I want to achieve is effectively the following:

myParser parse "/Users/jothi/Projects/Private/scala-projects/csv-parser/test.csv"

// but this works
myParser parse "/Users/jothi/Projects/Private/scala-projects/csv-parser/test.csv" using CSVParserConfig(Pipe)

So if the using CSVParserConfig is not provided, I should be able to box using defaultCSVParserConfig into the call!

But if the caller does not provide a specific config, I should apply the default as specified in the implicit

implicit def parser2parsed[B](parser: ReaderWithFile[B]): Seq[B] = parser.using(defaultParserCfg)

[Oliver Ruebenacker]

  If the expression would appear in a context where Seq[A] is required, then the implicit conversion would apply (for example, if you add a ": Seq[A]" at the end. BTW, what is A? It's nowhere defined.

  Otherwise, why not just add an argument with default value to the parse method?

[Joe San]

Adding a default argument would not let me write the call as expressive as it is now!