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constructorkotlin

Kotlin: 'val' on secondary constructor parameter is not allowed

I have following class:

class Person(val name: String) {
    private var surname: String = "Unknown"

    constructor(name: String, surname: String) : this(name) {
        this.surname = surname
    }
}

But when I want to have the name parameter immutable in second constructor:

constructor(val name: String, surname: String) : this(name) {
    this.surname = surname
}

I have the following compile-time error:

Kotlin: 'val' on secondary constructor parameter is not allowed

Can someone explain why is Kotlin compiler not allowing to do this?

Solution

  • Parameters in Kotlin are always immutable. Marking a constructor parameter as a val turns it into a property of a class, and this can only be done in the primary constructor, because the set of properties of a class cannot vary depending on the constructor used to create an instance of the class.