How do you make it not format out default values?

[kaihendry]

Can it make it NOT emit the default count of 5 here?

pkl eval -f json c.pkl 
{
  "bar": {
    "count": 5,
    "name": "hello"
  }
}

Wanted:

{
  "bar": {
    "name": "hello"
  }
}

❯ cat test.pkl 
module foo

bar: Bar;

class Bar {
        count: UInt16 = 5;
        name: String;
}

❯ cat c.pkl 
amends "test.pkl"

bar {
        name = "hello";
}

Thank you!

[StefMa]

You're looking for local properties.
See https://pkl-lang.org/main/current/language-reference/index.html#local-properties

Your test.pkl would then looks like this:

module foo

bar: Bar;

class Bar {
        local count: UInt16 = 5;
        name: String;
}

[kaihendry]

But when count is defined (and not default), it's not allowed with local!

❯ pkl eval -f json c.pkl
–– Pkl Error ––
Cannot find property `count` in object of type `foo#Bar`.

5 | count = 11;
    ^^^^^
at c#bar (file:///Users/hendry/docebo/traffic-control-pkl/tmp/c.pkl, line 5)

Available properties:
name

106 | text = renderer.renderDocument(value)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
at pkl.base#Module.output.text (https://github.com/apple/pkl/blob/0.27.2/stdlib/base.pkl#L106)


traffic-control-pkl/tmp on  main (e014805) [$?]
❯ cat c.pkl
amends "test.pkl"

bar {
	name = "hello";
	count = 11;
}

[bioball]

Generally, you'll want to make this a nullable property, and describe what it means if null as a doc comment.

Something like:

class Bar {
  /// Etc etc what count does  
  ///
  /// Default if not set: `5`
  count: UInt16?

  name: String
}

By default, the JSON renderer will omit null properties (see https://pkl-lang.org/package-docs/pkl/current/base/JsonRenderer.html#omitNullProperties).

Here's an example of another module that uses this pattern: https://github.com/apple/pkl-pantry/blob/fa1f4ad2889e10570a734f8b3fd4a68407d0b563/packages/com.influxdata.telegraf/plugins/inputs/PrometheusInput.pkl#L97