Add support for lenses generation for value classes #941
Description
Motivation
Good domain modelling requires the use of value classes. Those are currently not supported by our automatic lenses generator. So there is a mismatch between good practises and the ease of our framework.
Look at this example:
@JvmInline
value class Name(val value: String)
@JvmInline
value class Year(val value: Int)
@Lenses
data class Person(val name: Name, val yearOfBirth: Year) {
companion object
}As we can only annotate the data class, we can only map the root-store as follows:
val storedPerson = storeOf(Person(Name("Chris"), Year(1978)))
val storedName: Store<Name> = storedPerson.map(Person.name())In order to bind such a mapped store to some kind of UI element like an input, we need to access the value of the Name-type:
inputText {
// wont work! we nned some `String` and no other type!
value(storedName.data)
// we need something loíke this:
value(storedName.map(lensOf(
"",
getter = { v -> v.value },
setter = { _, v -> Name(v) }
)))
}As this is rather clumsy, we should enhance our generator to support value classes!
Proposal
We could easily extend the @Lenses-annotation to support value classes like that:
@Lenses
@JvmInline
value class Year(val value: Int) {
companion object
}
@Lenses
@JvmInline
value class Name(val value: String) {
companion object
}
// within the `generated` section
fun Year.Companion.value(): Lens<Year, Int> = lensOf(
"",
getter = { p: Year -> p.value },
setter = { _: Year, v: Int -> Year(v) }
)
// we could specifically support the formatting `lensOf`-factory if the target type is `String`:
fun Name.companion.value(): Lens<Name, String> = lensOf(
format = { p: Name -> p.value },
parse = { v: String -> Name(v) },
)