Is it possible to use a private secondary constructor to assign a val in Kotlin?

Issue

I am trying to reduce code repetition by using a private constructor to assign a class field, but this does not seem to be possible.

What I'm trying to do is the exemplified here:

class Foo {
    private val bar: Int
    private val baz: Int

    constructor(bar: Int, baz: Int) : this(baz) {
        this.bar = bar
    }

    constructor(bar: String, baz: Int) : this(baz) {
        this.bar = bar.toInt()
    }

    private constructor(baz: Int) {
        this.baz = baz
    }
}

The alternative, that works, but which I am not satisfied with is doing the following:

class Foo {
    private val bar: Int
    private val baz: Int

    constructor(bar: Int, baz: Int) {
        this.bar = bar
        this.baz = baz
    }

    constructor(bar: String, baz: Int) {
        this.bar = bar.toInt()
        this.baz = baz
    }
}

To be clear I am not satisfied because of the replication of the this.baz assignment.

Is this simply not possible in Kotlin, or am I missing something?

Solution

You should rewrite this as:

class Foo(
    private val bar: Int,
    private val baz: Int, 
) {
    constructor(bar: String, baz: Int) : this(bar.toInt(), baz)
}

The (Int, Int) constructor has been made into a primary constructor, initialising all the values. And the second constructor delegates the primary constructor.

The first two secondary constructors that you declared in your non-working code cannot reassign the vals, because they delegate to another constructor, and it is assumed that that constructor initialises all the necessary properties. Though in this case, it doesn't, so you get another error.

Answered By - Sweeper