Chainable Actors Extension

[limbusdev]

Hi,
would it be possible to extend Actors to make them chainable?

What we have now:

var myActor = Group()
myActor.setPosition(4f,5f)
myActor.setSize(5f,5f)

I have an extension:

fun Actor.lSetSize(width: Float, height: Float): Actor
{
    this.setSize(width, height)
    return this
}

fun Actor.lSetPosition(x: Float, y: Float, align: Int): Actor
{
    this.setPosition(x, y, align)
    return this
}

which changes that to

var myActor = Group()
myActor
    .lSetPosition(5f,4f)
    .lSetSize(5f,5f)

Problem is, this extension always returns objects of class Actor, not of the inheriting class. Any ideas?

And would you consider ding something similar in libKTX? Or, alternatively, would it be possible to have more Actor-inheriting classes to be defined at top level like tables?

image {
    drawable=pathToDrawable
    position = Vec2(3f,5f)
    ...
}

[jcornaz]

this extension always returns objects of class Actor, not of the inheriting class. Any ideas?

You can use generics

fun <T : Actor> T.lSetSize(width: Float, height: Float): T {
    this.setSize(width, height)
    return this
}

However, I would personnally not create such extensions, and use apply instead:

var myActor = Group().apply {
  setPosition(5f,4f)
  setSize(5f,4f)
}

Or, alternatively, would it be possible to have more Actor-inheriting classes to be defined at top level like tables?

I may be wrong, but I have the impression that it is already provided by the ktx-scene2d module.

[czyzby]

I advise against writing custom this-returning extension for every setter that you plan on using. This approach comes from Java, which lacks the DSL capabilities of Kotlin. Look into apply or let from the standard library, as @jcornaz mentioned - this would be the idiomatic Kotlin approach.

And would you consider doing something similar in libKTX?

ktx-scene2d and ktx-vis provide a very similar API using Kotlin type-safe builders DSL. We actually support 100% of LibGDX API, since we didn't write any setter wrappers, but instead provide similar this access as the apply would. Think of these as syntax sugar for defining actors. Go through their guides, and don't hesitate to ask if you've got any questions.

Does this solve your problem?

[limbusdev]

Yeah, thank you. I'm still new to kotlin and didn't know about apply. Thank you for your help. You can close, if you like :)