Is there a way to create an instance of a generic type in Scala other than reflection

Question

I am new to scala and after reading the scala tour I started working on a simple project to practice a bit.

In my project I wanted to extend the functionality of the Seq trait by making a implicit class that would wrap Seq and add some functionality on top.

My problem is something like this:

  implicit class wrapper[S[X] <: Seq[X], E](seq : S[E]) {
    def funkyFunc : S[S[E]] = {
      Seq[S[E]](seq)
    }
  }

This code won't compile because the compiler cant cast Seq[S[E]] to S[S[E]], so I tried to use casting like this:

  implicit class wrapper[S[X] <: Seq[X], E](seq : S[E]) {
    def funkyFunc : S[S[E]] = {
      Seq[S[E]](seq).asInstanceOf[S[S[E]]]
    }
  }

But now I the problem is at run time, when I try to pass a type that extends from Seq but list cant be cast into him we will get an exception.

I can't create an instance of type S[S[E]] because Seq doesn't have a contractor.

So is there a solution that I am missing that will let me get a behavior like this one:

  implicit class wrapper[S[X] <: Seq[X], E](seq : S[E]) {
    def funkyFunc : S[S[E]] = {
      S[S[E]]() :+ seq
    }
  }

Edit : I am using scala 2.13

Answer 1

Try

import scala.collection.Factory

implicit class wrapper[S[X] <: Seq[X], E](seq : S[E]) {
  def funkyFunc(implicit f: Factory[S[E], S[S[E]]]) : S[S[E]] = {
    Seq(seq).to(f)
  }
}

List(1, 2, 3).funkyFunc // List(List(1, 2, 3))