Update immutable data structure through inheritance

Question

I'm making a strategic game and I try to apply what I learned, try to use immutable data. In my game I have Units, these units can have different special function. By exemple some plane can hide themselves. What I search is a way to be able to do some sort of

abstract class Units {
val life:Int
}

trait Hidable { self: Units => 
val hided:Boolean
def hide:Units with Hidable= ....
}

without having to copy paste:

def hide = copy(hided=true)

on every case class that mixin Hidable.

So make it mutable, but only within the class, so you can change it. — James Black
– James Black, Commented Nov 11, 2012 at 1:42
Only metaprogramming with macros or toolboxes can help you, since the copy method of each case class is generated by compiler. You can learn more about it here: stackoverflow.com/questions/10373318/… — Nikita Volkov
– Nikita Volkov, Commented Nov 11, 2012 at 1:54

Community · Accepted Answer · 2017-05-23 11:56:11Z

1

A common way to update an immutable data structure -- is using lenses. There's a compiler plugin to generate lenses for your code, though it is not very production-ready. It is also available for an old scalaz only.

Here's a related question.

edited May 23, 2017 at 11:56

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answered Nov 11, 2012 at 11:26

George

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2 Comments

Atol Over a year ago

I use the latest scalaz, and if it's to add manually a Lense for a single field, I better cp: copy :(

George Over a year ago

If you are to modify a single field, you'll get by with a copy. If at some point you end up updating a deeply nested structure, lenses are a way to go. You can modify that compiler plugin to generate lenses in a way, scalaz-seven specifies. The difference isn't than big: the old way: gist.github.com/1404336#file_lens.scala, the new way: github.com/folone/poi.scala/blob/master/src/main/scala/info/…. Or create a plugin of your own, using macros.

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