Define class with variable number of properties

[ghyatzo]

Hello,

I was wondering if it was possible to create a type that must have a property, but otherwise its dynamic. 
 For example:

class Example {
    description: String
    // Some sort of "Varargs" property definition.
}

example = new Example {
    description = "this is a test"
    
    additional_prop = "I am"
    another_prop = "flattening"
    last_prop = "a listing"
}

This question raised when I was trying to generate a pkl file that would emulate a TOML configuration file that has some tables of the form:

[[examples]]
description = "this is always here for all tables"
arbitrary_key1 = "blah  blah"
abritrary_key2 = "blih bloh"

[[examples]]
description = "this is always here for all tables"
another_arbitrary_key1 = "..."
another_arbitrary_key2 = ",,,"
another_arbitrary_key3 = ";;;"

# and so on

I could simply add a listing property in the class Example, but then it wouldn't be flat anymore in the rendered TOML file, but instead have an extra table

[[examples]]
description = ...

[examples.keys]
arbtrary_key1 = ...
...

[HT154]

This isn't currently possible in Pkl. One way this sort of pattern can be implemented is via output converters:

class Example {
    description: String
    extraProperties: Dynamic // or Mapping, as appropriate
}

example = new Example {
    description = "this is a test"
    extraProperties {
        additional_prop = "I am"
        another_prop = "flattening"
        last_prop = "a listing"
    }
}

output {
    renderer {
        converters {
            [Example] = (it) -> it.toMap().remove("extraProperties") + it.extraProperties.toMap().remove("description")
        }
    }
}

[StefMa]

You're missing converters 🙃.
Still, it doesn't look correct. See https://pkl-playground.vercel.app/?share=instance-fence-blue

Or as an image for better reference:

[HT154]

Heh that's what I get for freehanding it before my morning coffee. Should be fixed now.

[ghyatzo]

Thanks a lot!
I suspected I had to use converters, but couldn't really wrap my head around on the how.
Super helpful as usual @HT154 !

P.S.: The last .remove("description") is not needed