Init a property with a setter in a primary constructor in Kotlin

Question

I have the following code:

class Camera : AsyncActiveInputDevice<Image> {
    constructor(inputListener: ((Image) -> Unit)? = null) {
        this.inputListener = inputListener
    }

    override var inputListener: ((Image) -> Unit)?
        set(value) {
            field = value
            TODO("call C/Python implementation")
        }
}

And IntelliJ IDEA is suggesting converting the constructor to a primary constructor.

So how to convert this? How to init a property with a setter in a primary constructor? I have tried init blocks but it then shows an error: "Variable can not be initialized before declaration".

score 2 · Accepted Answer · answered Nov 26 '18 at 08:20

2

Such a primary constructor would go in the header of the class, like this:

class Camera(inputListener: ((Image) -> Unit)? = null) : AsyncActiveInputDevice<Image> {

    override var inputListener: ((Image) -> Unit)? = inputListener
        set(value) {
            field = value
            TODO("call C/Python implementation")
        }

}

You can get this conversion done by the IDE by invoking intention actions on the warning (Alt + Enter on Windows, ⌥↩ on macOS), and choosing Convert to primary constructor.

answered Nov 26 '18 at 08:20

zsmb13

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Expanding on this: Custom getters and setters aren't supported in the primary constructor because [there wasn't/isn't a good syntax to implement the feature with](https://discuss.kotlinlang.org/t/private-setter-for-var-in-primary-constructor/3640/2) – Zoe Nov 26 '18 at 14:52

score 2 · Answer 2 · answered Nov 26 '18 at 08:25

The init block must come after the variale declaration. That's what the error message is telling you:

class Camera(inputListener: ((Image) -> Unit)? = null): AsyncActiveInputDevice<Image> {

    override var inputListener: ((Image) -> Unit)? = inputListener
        set(value) {
            field = value
            TODO("call C/Python implementation")
        }


    init {
        this.inputListener = inputListener
    }
}

Init a property with a setter in a primary constructor in Kotlin

2 Answers2