The Item class has an instance variable id that starts with 0. I want to call nextID to increment the id from 0 to 1; however, when i do new Item().id += 1, there is a type mismatch. Why is that?
class Item { private var id: Int = 0 this.id = Item.nextId } // companion object object Item{ def apply() = new Item() def nextId: Int = { new Item().id += 1 //type mismatch } } Where to begin?
def nextId: Int = { new Item().id += 1 } += is an assignment. Assignments don't have return values but nextId is supposed to be an Int. We might fix it like this...
def nextId: Int = { val nitem = new Item() nitem.id += 1 nitem.id } ...but there are other problems. Every time someone invokes nextId it creates a new Item, that Item's id is incremented, the updated value of this id is returned, and the new Item is thrown away. That doesn't sound right.
class Item { private var id: Int = 0 this.id = Item.nextId } Hmm, this looks suspicious. When an Item is created it calls nextId, but nextId creates a new Item, which is going to call nextId, which creates a new Item, which calls .... where will it all end?
id a val. Initialize it to the only value it will ever have when it is created. The companion object should hold the private var that is the id counter. Then all that nextId() has to do is increment the counter and return the new value.
this.id = Item.nextId?+=returnsUnitso that's why you have a type mismatch, but that's not the only problem you have herenextIdis supposed to return anInt, but this expressionnew Item().id += 1returnsUnit, because that's what+=returns. Check this post for a possible solution: stackoverflow.com/questions/1888716/…. Moreover, I do not think you have to create a new Item insidenextId.