File system class structure in scala

Question

What would be the appropriate way to implement a file system class structure in scala?

I want the Root to be a Directory and to have itself as a parent.

import scala.collection.mutable

sealed trait Entry
class Directory(val parent: Directory, val content: mutable.IndexedSeq[Entry]) extends Entry
class File(val parent: Directory, val content: String) extends Entry
object Root extends Directory(Root, mutable.IndexedSeq[Entry]())

The attempt above results in:

Error:

(23, 31) super constructor cannot be passed a self reference unless parameter is declared by-name object Root extends Directory(Root, IndexedSeq())

It would be empty in the beginning, but you could add entries to Root.content. — senjin.hajrulahovic
– senjin.hajrulahovic, Commented Mar 11, 2019 at 19:44
Can you say what is your goal? Why do you need bi-directional references? — Krzysztof Atłasik
– Krzysztof Atłasik, Commented Mar 11, 2019 at 21:01
I would like e.g. to list all entries of a directory but would also like to print a parent directory of a file/directory. — senjin.hajrulahovic
– senjin.hajrulahovic, Commented Mar 11, 2019 at 21:08

jwvh · Accepted Answer · 2019-03-12 08:06:14Z

1

One thing you could do is create a 2nd trait just for directories.

import scala.collection.mutable.ArrayBuffer  // easier to update

sealed trait Entry
sealed trait Directory extends Entry {
  val parent  :Directory
  val content :ArrayBuffer[Entry]
}

class File(val parent  :Directory
          ,val content :String) extends Entry

class SubDir(val parent  :Directory
            ,val content :ArrayBuffer[Entry]) extends Directory

object Root extends Directory {
  override val parent  :Directory = this
  override val content :ArrayBuffer[Entry] = ArrayBuffer()
}

Now you can create/update directory contents, and the parent of Root is still Root.

Root.content += new File(Root, "name")
Root.content += new SubDir(Root, ArrayBuffer())

Root.parent.parent.parent  //res2: Directory = Root$@294c7935

answered Mar 12, 2019 at 8:06

jwvh

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1 Comment

senjin.hajrulahovic Over a year ago

Seems reasonable. Thanks.

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