Null / undefined Handling

[AugustNagro]

Currently we're not handling null/undefined at all. One way we could is to make 3 new typeclass instances (one for A | Null, one for A | Unit, and one for A | Null | Unit).

For example:

given [A](using nc: NativeConverter[A]): NativeConverter[A | Null | Unit] with
      extension (t: A | Null | Unit) def toNative: js.Any =
        if t == null || t == () then t.asInstanceOf[js.Any]
        else nc.toNative(t.asInstanceOf[A]) // if there was flow-typing for Unit there would be no need to cast :'(

      def fromNative(nativeJs: js.Any): A | Null | Unit =
        if nativeJs == null || js.isUndefined(nativeJs) then nativeJs.asInstanceOf[Null | Unit]
        else nc.fromNative(nativeJs)

    val nc3 = NativeConverter[Int | Null | Unit]
    assertTrue(nativeNull == nc3.toNative(null))
    assertTrue(js.undefined == nc3.toNative(()))
    assertTrue(JSON.parse("5") == nc3.toNative(5))

    assertTrue(null == nc3.fromNative(nativeNull))
    assertTrue(() == nc3.fromNative(js.undefined))
    assertTrue(5 == nc3.fromNative(JSON.parse("5")))

    case class C(c: Int | Null | Unit) derives NativeConverter
    val nullC = C(null)
    assertEquals(""" {"c":null} """.trim, JSON.stringify(nullC.toNative))
    assertEquals(nullC, NativeConverter[C].fromNative(JSON.parse(""" {"c":null} """)))
    val undefC = C(())
    assertEquals(""" {} """.trim, JSON.stringify(undefC.toNative))
    assertEquals(undefC, NativeConverter[C].fromNative(JSON.parse(""" {} """)))
    val intC = C(123)
    assertEquals(""" {"c":123} """.trim, JSON.stringify(intC.toNative))
    assertEquals(intC, NativeConverter[C].fromNative(JSON.parse(""" {"c":123} """)))

However, no flow-typing for Unit makes this inconvenient.

lampepfl/dotty-feature-requests#178

[evbo]

Hit this just now ;) Would what you propose also support Option types?

Such as if the value is completely missing from the Json it assumes a value of None instead of js.Undefined or null? That is how circe works and it's a great way to make a smaller footprint Json file by dropping nulls while keeping idiomatic Option types

[AugustNagro]

Option is already supported, see https://github.com/getshaka-org/native-converter#option and https://github.com/getshaka-org/native-converter/blob/master/js/src/test/scala/JsonTests.scala#L226

This issue is specifically for union types.

If you're having a problem with Options, please make a new issue.

[evbo]

You're right, they work great! I misread this was how undefined Json attributes should be handled, but like you say you can also use Option types. Thanks for setting me straight :D

[AugustNagro]

Yes, it would be good to have a NativeConverter instance for (A | Unit) or maybe js.UndefOr.