kotlinextension-function

Why cannot I create extension to BigDecimal in Kotlin?

I am trying to create an extension as a property and I experimented with an extension function as well, below an example for BigDecimal:

val BigDecimal.HUNDRED: BigDecimal
    get() = TEN.multiply(TEN)

fun BigDecimal.HUNDRED_ONE(): BigDecimal {
    return TEN.multiply(TEN)
}

It seems that Kotlin recognizes neither HUNDRED nor HUNDRED_ONE(). I am using Kotlin version 1.5.21.

Am I doing anything wrong on Kotlin version 1.5.21 that doesn't work correctly?

I have used this functionality before for lists. For instance:

fun <T> toList(list: List<T>?): List<T> {
    return list ?: listOf()
}
Solution

  • I assume you wanted to use it like this:

    val value = BigDecimal.HUNDRED

    As far as I know, this is not possible in Kotlin right now. Extensions work on instances, so they're more like instance members, not static members. With your above code this will work: BigDecimal(0).HUNDRED.

    I believe there is only one situation when it is possible to provide "static" extensions. If class has a companion (so it is Kotlin class) then we can add extensions to this companion. But this is not at all applicable to BigDecimal or any other Java class.