Is there a way to have a data class secondary constructor provide a value for a non-primary-construc...

# getting-started

[Paul Griffith]

Is there a way to have a data class secondary constructor provide a value for a non-primary-constructor val ? 🧵 ->

[Paul Griffith]

I want to have a val member of the class that is, if you call the primary data class constructor, null, or if you use the secondary constructor, whatever you supplied. I do not want this field to be in equals/hashcode...but I also don't really want to write my own equals & hashcode, and this seems reasonable (albeit an edge case)

[Paul Griffith]

This is the 'best' workaround I can come up with, by using a secondary property

Untitled.kt

[Joffrey]

Why don't you just remove the secondary constructor, and provide deferredType with null default value in the primary constructor?

data class Attribute constructor(
        override val name: String,
        override val location: String,
        override val description: String? = null,
        override val kind: Kind = Kind.INSTANCE_MEMBER,
        private val deferredType: TypeSupplier? = null,
) : CompletionDescriptor()

[Paul Griffith]

It'll still be used in the autogenerated`equals` and hashcode in that case, and TypeSupplier is a SAM with no meaningful equals/hashcode implementation

[Paul Griffith]

Some kind of @Omit annotation would be ideal but searching this Slack makes it seem like the official suggestion is just to override equals & hashcode yourself

[Joffrey]

Good point, in that case your solution seems appropriate, nothing comes to mind at the moment

[Paul Griffith]

Which is fair, like I said, this is an edge case

[Joffrey]

Oh wait I just realized you could simply make the setter private for `deferredType`:

data class Attribute constructor(
        override val name: String,
        override val location: String,
        override val description: String? = null,
        override val kind: Kind = Kind.INSTANCE_MEMBER,
    ) : CompletionDescriptor() {
        override var deferredType: TypeSupplier? = null
            private set

        constructor(
            name: String,
            location: String,
            description: String? = null,
            kind: Kind = Kind.INSTANCE_MEMBER,
            deferredType: TypeSupplier? = null,
        ) : this(
            name, location, description, kind
        ) {
            this.deferredType = deferredType
        }
}

[Paul Griffith]

That's elegant enough for me, good stuff