Hello! I have a little doubt. When I try to modify a field Option <String>, this is replaced b...

# arrow

[carbaj0]

Hello! I have a little doubt.
When I try to modify a field Option <String>, this is replaced by a String instead of a Option<String>

ej : data class PersonalDataModel(
    val firstName: Option<String>
)

firstName.modify(state){ //here i have a String instead of Option<String> }

[simon.vergauwen]

Are you using generated optics?

The reason for that is that an Optional is generated instead of a Lens.

https://arrow-kt.io/docs/0.10/optics/lens/
https://arrow-kt.io/docs/0.10/optics/optional/

Optional is a combination of copy with when to modify or getOption the focus.

[carbaj0]

@optics
data class PersonalDataModel(
    val firstName: InputModel,
    val secondName: InputModel,
    val firstLastName: InputModel,
    val secondLastName: InputModel,
    val birthDate: SpinnerModel,
    val nationality: SpinnerListModel,
    val birthPlace: Option<SpinnerModel>,
    val gender: SpinnerListModel
) {
    companion object
}

val initialState = PersonalDataModel(
           ......... ,
            birthPlace = None
        )

model.birthPlace.modify(state) { SpinnerModel("Birth Place", {}) } }

[carbaj0]

this i think that return None instead of the new object

[simon.vergauwen]

That’s because you cannot apply f of modify over None

[carbaj0]

What would the best approach to modify the initial None state?

[simon.vergauwen]

In that case you probably want to use a Lens<PersonalDataModel, Option<SpinnerModel>> or Lens<PersonalDataModel, SpinnerModel?>.

Which currently is not autogenerated.
The reason you want to model it with a Lens instead of a Optional is because you then have the ability to control the Option rather than using the non-nullable SpinnerModel in Optional.

[simon.vergauwen]

All the is used underneath is how you’d write it by hand.

In the case of Lens you’re dealing directly with the properties of a data class and you can set or get them, abstracting over properties and copy.

In the case of Prism you’re dealing with the properties of a subtype of a sealed class. This abstracts over when and copy, and it thus not have the same powers as Lens. Instead it can getOption the result from when or it attempt to modify if the correct subtype is found using when .

An Optional is the composition of a Prims and Lens which thus it has the same limitations as both combined.

[carbaj0]

perfect I going to dig into all this stuff, I have used the optics annotation because is the least boilerplate implementation