Say I've got a World class. A world can contain Sp...

# getting-started

[Paul N]

Say I've got a World class. A world can contain Spheres, and a Sphere can have properties such as Colour. So on my World class I have a factory function within a companion object called defaultWorld. This returns me an instance of a World with two Colour.RED Spheres.

What's the best way of taking a defaultWorld and modifying it so that, for example, one of the Sphere's is Colour.BLUE not RED ?

At the moment all the attributes of Sphere are val's not vars, so I can't just do world.spheres[0].colour=Colour.BLUE. And even if I did change it to var, that changes the defaultWorld for everything.

So what's the best way of having some sort of template object that I can easily create new variants from ?

[Shawn]

It kind of depends - you could rely on mutable state and access the World members via locks or some other mutual exclusion mechanism, or maybe you could generate a new World with the spheres you need and replace the old World with this new one

[Shawn]

how are you storing the spheres? are they just members of the class or are they in a queue or another similar structure?

[karelpeeters]

Or maybe look into a World builder with defaults?

[Casey Brooks]

data classes have a generated copy() method, and you can use its named arguments to only change some of its properties on copy

[Brandon Trautmann]

I would use data class copy like @Casey Brooks mentioned above if the number of spheres is finite...

[marstran]

If you have a deeply nested structure of data classes, I would take a look at optics in Arrow.