Hello I m trying to do something like this and not sure what

Question

Hello I m trying to do something like this and not sure what I m doing I want to have a Factory of let s say Ship A Game has a mutable list or whatever of Ships so I can track all the Ships in my game more in thread gt

Amir Eldor · Answer

The Factory gets a reference to Game when I first create it and when building a Ship the Factory registers the Ship in its Game reference However the developer can still create classes of Ship outside the factory I know I can give Ship a private constructor but how would I allow the factory to create Ships that way If I use a companion object I will need to provide it with the Game reference each time and it kind of loses the purpose of creating the Factory with the Game reference once In C++land I d probably use friend or something like that How do you do that in Kotlin Thanks

Amir Eldor · Answer

Or maybe there s a smarter way to solve the let s track all Ships problem

nanodeath · Answer

gt However the developer can still create classes of Ship outside the factory is this a feature or a bug

Amir Eldor · Answer

It s a bug as this way Game will not track the new Ship

Amir Eldor · Answer

That s why I want to centralize the creation of Ship in a Factory with a reference to a game there may be different games at the same time

Amir Eldor · Answer

Maybe there s a trick with the `internal` keyword but maybe I m barking at the wrong tree

nanodeath · Answer

depends on whether you want people to be able to subclass Ship if no then saying `class Ship internal constructor ` should be sufficient then making `ShipFactory newShip ` public

nanodeath · Answer

if yes subclassing permitted you maybe could make `Ship` itself accept `Game` as a constructor argument that Ship registers with in the constructor but passing `this` to other objects from a constructor is problematic from various perspectives security exception handling

nanodeath · Answer

or finally just say hey you have to call `Game addEntity ship ` or it ain t gonna work

Amir Eldor · Answer

Ok cool so two question

Amir Eldor · Answer

I made the internal Ship class inside package `a stuff game` but when I created a Ship instance in `a stuff somethingelse` the compiler did not complain Is this expected as the `a stuff` is common

nanodeath · Answer

`internal` works pretty differently from `package private` `internal` is accessible anywhere in the entire compilation unit e g your library engine

nanodeath · Answer

if your game and engine are in the same compilation unit and you re trying to keep yourself from calling the Ship constructor directly that s going to require more thought

nanodeath · Answer

internal is documented <https kotlinlang org docs reference visibility modifiers html modules|here>

Amir Eldor · Answer

Yeah I ve read this by module they mean compilation unit

Amir Eldor · Answer

gt `internal` any client inside this module who sees the declaring class sees its `internal` members

nanodeath · Answer

yeah module as in like a Gradle project subproject

Amir Eldor · Answer

I mistook that for package alright Thanks

nanodeath · Answer

I keep thinking package but that s a ridiculously overloaded term

nanodeath · Answer

I don t care much for Scala but it s ridiculously fine grained access controls were nice sometimes slightly smiling face

Amir Eldor · Answer

I didn t have the pleasure to play with Scala not sure if I will sweat smile

Amir Eldor · Answer

Regarding Ship registering itself in game in a constructor there s no real safe way to do that because the Ship s `this` is incomplete

Amir Eldor · Answer

I read about some lateinit magic but not sure if that s a thing

nanodeath · Answer

lateinit is for certain var fields set outside the constructor

Amir Eldor · Answer

And well bottom line I think the best way is just to register the Ship manually after creating it or inside a Factory OR go the ECS route and be a happier person

nanodeath · Answer

incidentally the ECS route also probably requires you explicitly registering some things with the World I m writing an ECS for KorGE right now and running into that systems and components have to be manually registered with World which sucks

Amir Eldor · Answer

Hello KorGE nice to meet you

Amir Eldor · Answer

Although I m creating something a bit different

Vampire · Answer

Make the constructor private and make the factory method in the companion object

nanodeath · Answer

I ve found `private` to be way stricter than Java s `private` when it comes to inner classes and the like

Vampire · Answer

Even if so Companion object can pretty well access the private constructor

Vampire · Answer

Amir Eldor · Answer

< Vampire> can I create a companion object with a reference to a `Game` so every call to companion s buildShip could reference that Game I initially gave

Vampire · Answer

You can set a property of the companion object

Amir Eldor · Answer

Like that

Vampire · Answer

Yeah that works too I had something in mind like untested written on mobile ```kt class Ship private constructor Tickable companion object lateinit val game Game fun create = Ship also game register override fun tick println tock Ship game = Game Ship create ```

Amir Eldor · Answer

Thanks looks cool But this way Ship is tied to a single Game instance right I might have another game running in parallel which needs ships created in it and not the former

Vampire · Answer

Yeah then the property approach doesn t work of course so something like you have or like this ``` Yeah that works too I had something in mind like untested written on mobile ```kt class Ship private constructor Tickable companion object fun producer game Game gt Ship = Ship also game register override fun tick println tock Ship game = Game Ship create ```

Amir Eldor · Answer

thanks I ll look into that fancy also syntax too