Is there a way to use the default value on a non-optional parameter when null is passed?

Question

For example, if I have the following data class:

data class Data(
    val name: String = \"\",
    val number: Long = 0
)

And functions that ca

Answer 1

the secondary constructor only supports for the Nullable primitive properties. which means it will result in 2 same constructors if the property is not a primitive type, for example:

data class Data(val name: String) {
    constructor(name: String? = null) : this(name ?: "foo");
    // ^--- report constructor signature error                
}

data class Data(val number: Long = 0) {
     constructor(number: Long? = null) : this(number ?: 0)
     //                  ^--- No problem since there are 2 constructors generated:
     //                       Data(long number) and Data(java.lang.Long number)
}

an alternative way is using invoke operator for that, for example:

data class Data(val name: String) {
    companion object {
        operator fun invoke(name: String? = null) = Data(name ?: "")
    }
}

IF the class is not a data class, then you can lazy initializing properties from parameters, rather than define properties on the primary constructor, for example:

class Data(name: String? = null, number: Long? = null) {
    val name = name ?: ""
    val number = number ?: 0
}

Answer 2

You can define a companion object for your data class and overload its invoke operator to use default values when null is passed:

data class Data private constructor(
    val name: String,
    val number: Long
) {
    companion object {
        operator fun invoke(
            name: String? = null,
            number: Long? = null
        ) = Data(
            name ?: "",
            number ?: 0
        )
    }
}