Reusing parent class object in subclass object

[sake92]

Hello!
I am making an experimental build tool called Deder, and using Pkl as its config language.

Here is the project config definition and example usage.

TLDR I have:

abstract class DederModule 
open class ScalaModule extends DederModule
class ScalaTestModule extends ScalaModule
modules: Listing<DederModule>

// and then using these
local const baseModule: ScalaModule = new { ..
local const common = (baseModule) {
// but i cant do this...
local const uberTest: ScalaTestModule = (baseModule) {

Is there a way to cast/spread the baseModule as a ScalaTestModule ?

[HT154]

Like many OO languages, there isn't a direct way to do this. That said, it is actually possible in Pkl and you're on the right track with spreading:

local const uberTest: ScalaTestModule = new {
  ...baseModule.toDynamic()

[sake92]

Thanks, I did try this. It seems to works for simple cases, but not like this for example:

abstract class DederModule {
  id: String
}

open class ScalaModule extends DederModule {}

class ScalaTestModule extends ScalaModule {}

local const baseModule: ScalaModule = new {}
local const scalaModule = (baseModule) { id = "base-module" }

// but i cant do this...
local const scalaTestModule: ScalaTestModule = new {
  ...baseModule.toDynamic()
  id = "uber-test-module"
}

modules: Listing<DederModule> = new {
  scalaModule
  scalaTestModule
}

fails with this error:

(base) sake:~/projects/tmp/pkl-inheritance$ pkl eval bla.pkl 
–– Pkl Error ––
Tried to read property `id` but its value is undefined.

2 | id: String
    ^^
at bla#DederModule.id (file:///home/sake/projects/tmp/pkl-inheritance/bla.pkl, line 2)

20 | scalaTestModule
     ^^^^^^^^^^^^^^^
at bla#modules[#2] (file:///home/sake/projects/tmp/pkl-inheritance/bla.pkl, line 20)

106 | text = renderer.renderDocument(value)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
at pkl.base#Module.output.text (https://github.com/apple/pkl/blob/0.29.0/stdlib/base.pkl#L106)

107 | bytes = text.encodeToBytes("UTF-8")
              ^^^^
at pkl.base#Module.output.bytes (https://github.com/apple/pkl/blob/0.29.0/stdlib/base.pkl#L107)

[HT154]

Hmm that's a somewhat surprising error. I'd need to investigate a bit deeper to figure out if it's a bug.

That said, this works:

local const scalaTestModule: ScalaTestModule = (baseModule.toDynamic().toTyped(ScalaTestModule)) {
  id = "uber-test-module"
}

You could even make this more convenient:

abstract class DederModule {
  id: String

  fixed asScala: ScalaModule = this.toDynamic().toTyped(ScalaModule)
}

open class ScalaModule extends DederModule {
  fixed asTest: ScalaTestModule = this.toDynamic().toTyped(ScalaTestModule)
}

class ScalaTestModule extends ScalaModule {}

local const baseModule: ScalaModule = new {}
local const scalaModule = (baseModule) { id = "base-module" }

local const scalaTestModule: ScalaTestModule = (baseModule.asTest) {
  id = "uber-test-module"
}

modules: Listing<DederModule> = new {
  scalaModule
  scalaTestModule
}

[sake92]

Thanks! Yes this seems to work. I did try it before but got some confusing results. I think that's because I've used fixed type: String and that didn't change when I cast it to ScalaTestModule.

But with those functions I can neatly extract that code. Thanks for the tips!