Hi there! I'm trying to find if is possible in Kot...

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[Gerard Bosch]

Hi there! I'm trying to find if is possible in Kotlin to define a custom accessor for a class or data class that simply returns the non-nullable version of a class field (using a fallback value). Can't figure out how the syntax would be for the following:

data class MyDataClass(private val myProperty: BigDecimal?) {
            val myProperty: BigDecimal = myProperty 
                get() = field ?: BigDecimal.ZERO       // <-- I want to just expose the non-nullable version of the property
        }

👆 I've just tried the above as per what I could grasp from https://kotlinlang.org/docs/properties.html#getters-and-setters but can't make it work 😬

Is that possible to redefine a property accessor in such way? If it is, which syntax/construct should achieve it? Thx!

[Gerard Bosch]

I could to it using a function in the body of the class, but I would like to know if it is possible to do so using the same property as at call-site can be seen as a property instead of function call

fun myProperty(): BigDecimal = fxFeePercentage ?: BigDecimal.ZERO

[randomcat]

no, it's not

[randomcat]

you would need to pick a different name

[Gerard Bosch]

Ohh 😞 I thought that, but was not sure

[Gerard Bosch]

Thanks!

[randomcat]

np

[Gerard Bosch]

So probably the function approach suits me better then

[randomcat]

I wouldn't do that with the exact same name either even if it's possible

[randomcat]

at some point you'll type one and mean the other and you'll have a bad day

[Gerard Bosch]

The property is private, just want to expose it as non-nullable with a default value

[Gerard Bosch]

I've just got an idea! Maybe I can use a default value in the constructor, that would work for my case I think

[randomcat]

depends on the semantics you want

[nkiesel]

import java.math.BigDecimal

data class MyDataClass(private val _myProperty: BigDecimal?) {
    val myProperty: BigDecimal
        get() = _myProperty ?: BigDecimal.ZERO
}

fun main() {
    val p1: BigDecimal = MyDataClass(BigDecimal(22)).myProperty
    val p2: BigDecimal = MyDataClass(null).myProperty
    println("p1=$p1 p2=$p2")  // prints p1=22 p2=0
}

[Gerard Bosch]

Thanks for the naming idea @nkiesel - I'm totally new to Kotlin, but I see what you mean, should perfectly work as well

[nkiesel]

this could even use val myProperty: BigDecimal = _myProperty ?: BigDecimal.ZERO if the fallback value is constant

[Gerard Bosch]

👍 thx 🙂 🙂

[Marc Knaup]

Ideally data classes don’t change/compute their properties after creation.
Looks like you want to default null values to 0, so you could just provide a factory:

data class MyDataClass(val myProperty: BigDecimal)

fun MyDataClass(myProperty: BigDecimal?) =
    MyDataClass(myProperty ?: BigDecimal.ZERO)

[nkiesel]

only downside is that this then means the class has 2 fields instead of 1. Classical space/time trade-off

[Marc Knaup]

If you also need a copy() with nullable myProperty then you have to add your own copy() extension function too.