How can one implement mostly the same classes

[foreg]

Consider an on-premise service offering two subscription plans: Free and Paid. Both plans provide a set of common features as well as some specific. What is the correct way to express features property of this service in a template?

I tried this approach:

// template.pkl
open module template

class Feature {
  enabled: Boolean
}

abstract class Features {
  auth: Feature
}

class FreeFeatures extends Features {
  advertisement: Feature
}

class PaidFeatures extends Features {
  exporter: Feature
}

features: FreeFeatures|PaidFeatures

// free.pkl
extends "./template.pkl"

features {
  auth {
    enabled = true
  }
  advertisement {
    enabled = true
  }
}

but the evaluation on free.pkl gives me "Tried to read property features but its value is undefined."

[holzensp]

The default value of a type union is undefined, by default. If you want it to have a default, you have to annotate one of the alternatives with a * (see here).

Since features: FreeFeatures|PaidFeatures has no default value, there is nothing to amend when you say features {. In this case, you should either give it a default value upon its first use (in free.pkl):

features = new FreeFeatures {

of you give it one in the template.pcl:

features: *FreeFeatures|PaidFeatures

Mind you, there is general IDE degradation from using such unions; when I edit free.pkl, autocomplete for the body of features gives me both advertisement and exporter.

Also, why is free.pkl an extends of template.pcl and not an amends? Your editor experience and overall safety (from typos etc) is much better when you amends.

[foreg]

Thank you! features = new FreeFeatures { is what I was looking for.

Mind you, there is general IDE degradation from using such unions; when I edit free.pkl, autocomplete for the body of features gives me both advertisement and exporter.

I changed features' type to Features; it looks much better now

Also, why is free.pkl an extends of template.pcl and not an amends? Your editor experience and overall safety (from typos etc) is much better when you amends.

I used it to give myself the option to add another arbitrary property unique to free.pkl. What would be a better way to accomplish this?

Thank you once again for your help!