Multiple methods with same functionality but different types

Question

Using Scala, I have a network consisting of InputNodes and OutputNodes, which both extend a common trait NetworkNode. However, I want to implement the addition of a node within a manager class, which has separate private collections for different types of nodes. This is my first attempt:

  // Adds a node into the network, depending on type.
  def addNode(node: InputNode, name: String = "") = {
    if (!name.isEmpty()) {
      node.name = name
    }
    this.inputNodes += node
  }

  def addNode(node: OutputNode, name: String = "") = {
    if (!name.isEmpty()) {
      node.name = name
    }
    this.outputNodes += node
  }

However, there are two problems.

1) The code is essentially the same, yet I cannot add a NetworkNode to an ArrayBuffer[InputNode] and therefore need to be more specific with the type.

2) Overloading parameters with default values in the same position are not possible.

As I expect the code to grow, I'd like to get everything done in a single addNode function, which could use a match structure to select where to append the new node based on their type. This would resolve both problems, but how could I resolve the collection type issue? For example, the following doesn't work:

  // Adds a node into the network, type NetworkNode is the common parent.
  def addNode(node: NetworkNode, name: String = "") = {
    if (!name.isEmpty()) {
      node.name = name
    }

    // Say we deduce class based on a field called TYPE.
    node.TYPE match {
      case "input" => inputNodes += node    // node is a NetworkNode, not an InputNode!!!
      case "output" => outputNodes += node
      case _ => throw new Exception("Type " + node.TYPE + " is not supported!")
    }
  }

Thank you for the help!

Seems a classic scenario for subclasses and inheritance.

The Archetypal Paul
– The Archetypal Paul

2015-12-18 20:55:54 +00:00
Commented Dec 18, 2015 at 20:55 — The Archetypal Paul
– The Archetypal Paul, Commented Dec 18, 2015 at 20:55

Jonathan Nappee · Accepted Answer · 2015-12-18 20:09:10Z

1

This match does the type conversion for you.

// Adds a node into the network, type NetworkNode is the common parent.    
def addNode(node: NetworkNode, name: String = "") = {
 if (!name.isEmpty()) {
   node.name = name
 }

 node match {
   case x : InputNode  => inputNodes += x
   case x : OutputNode   => outputNodes += x
   case _ => throw new Exception("Type " + node.TYPE + " is not supported!")
 }
}

answered Dec 18, 2015 at 20:09

Jonathan Nappee

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2 Comments

Jonathan Nappee Over a year ago

By the way changing the name at the same time as adding to the collections seems strange.

mmKALLL Over a year ago

That seems so obvious now that I see it... Thank you for the fast response! I decided that I'd like to have the name as an optional parameter to make the GUI development more flexible and less troublesome. The nodes themselves have a default name assigned to them in their constructor, based on an ID. This way there's no need to use another line of code for assigning a custom name, or to make it a constructor parameter.

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