Creating a data class instance using secondary constructor with parameter which is another similar class

Question

I have a data class:

data class Person (
    val login: String,
    val password: String
)

Sometimes I need to instantiate it with my custom data, but sometimes I need to initialize my user by another class instance:

val authPerson = api.getAuthPerson()  // AuthPerson class has the same fields
val user = User(authPerson)

I wrote secondary constructor, but it doesn't work:

data class User (
    val login: String,
    val password: String
) {
    constructor(authPerson: AuthPerson) {
        login = authPerson.login;
        password = authPerson.password
    }
}

Can anybody advise me correct decision please?

Martin Marconcini · Accepted Answer · 2019-10-06 11:02:02Z

4

Or if you don't want to use a factory, you can do:

data class User (
    val login: String,
    val password: String
) {
    constructor(anotherUser: User): this(anotherUser.login, anotherUser.password)
}

Secondary Constructors must call their primary constructor.

answered Oct 6, 2019 at 11:02

Martin Marconcini

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Comments

Andrei Tanana · Accepted Answer · 2019-10-06 10:52:13Z

2

You can create a factory method:

data class User(
    val login: String,
    val password: String
) {
    companion object {
        fun fromPerson(person: Person) = User(person.login, person.password)
    }
}
...
val user = User.fromPerson(person)

or create an extension function:

fun Person.toUser() = User(login, password)
...
val user = person.toUser()

answered Oct 6, 2019 at 10:52

Andrei Tanana

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