How do I require an Any?

[ericzbeard]

I need to define a class with a required property that can be anything, but Any is apparently equivalent to Any?. This code fails, which is confusing because if I replace hidden Foo: Any with hidden Foo: Any?, it succeeds:

open class Test {
    hidden Foo: Any

    // This works
    // hidden Foo: Any?

    hidden Str: String
    
    Props {
        ["Foo"] = Foo
        ["Str"] = Str
    }
}

t = new Test {
    Foo {
        Bar = "Baz"
    }

    // This works
    // Foo = ""

    Str = ""
}

[ericzbeard]

Ok I think I figured this out.. just need to replace Any with Dynamic.

[bioball]

You want foo: NonNull; NonNull is defined as:

typealias NonNull = Any(!(this is Null))

[ericzbeard]

What's the difference between that and Dynamic?

[bioball]

Dynamic is its own leaf type, and doesn't permit other types. On the other hand, Any is the top type; it permits any value. NonNull is basically just Any that doesn't permit Null.

The following throws:

foo: Dynamic = 1

But this will succeed:

foo: NonNull = 1

Dynamic is a special type of object that allows any property, element, or entry. It's actually rarely used in normal Pkl. It's more common to define your data in terms of classes, mappings, and listings, which will give you validation. Dynamic is useful as an ad-hoc data type if you want to just start writing Pkl without the overhead of first defining a schema.

More details: https://pkl-lang.org/main/current/language-reference/index.html#typed-objects

[ericzbeard]

I think Dynamic is what I need. I'm modeling AWS CloudFormation registry schemas, which sometimes define properties as "object", which can be any valid YAML/JSON.

[ericzbeard]

The sample code still fails with NonNull

[bioball]

Gotcha!

For CloudFormation: we haven't published it anywhere, but: I've played around with using our JSON Schema generator to generate Pkl modules, and it works pretty well.

Here's a gist. You can clone this down somewhere, run bash download-schemas.sh, then run pkl eval convert.pkl to generate the Pkl output.

https://gist.github.com/bioball/9edf23a41695cb2080131ec3610a4c17

[ericzbeard]

Nice! I'll check that out. I already have schema processing for CloudFormation in Rain, working on pkl support in this PR. Fun project!

[bioball]

Awesome! That looks really cool!