Generics Question: I want to constrain a type in a...

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[tylerwilson]

Generics Question: I want to constrain a type in a class such that the type supports arithmetic operations, like so:

data class Item<T>(val operand1: T, val operand2: T) {
      val result: T = operand1 / operand2
}

But it gives me errors about BigDecimal (I guess this is the first class it tried to match. So I need to constrain T to be only types that support division, like T: Number, T: divideBy or something. Is this possible in Kotlin? Thank you!

[Andreas Sinz]

There is no way to do that sadly. You'd need a common interface that provides methods for the arithemtic operations that Int, Float etc. implements

[Andreas Sinz]

but there is none. Your best bet is to use ad-hoc polymorphism:

data class Item<T>(val operand1: T, val operand2: T, val operation: (T, T) -> T) {
    val result: T = operation(operand1, operand2)
}

[tylerwilson]

Bummer, that is what i suspected. I am currently checking types inside the methods, but it is ugly of course.I guess maybe I would write my own generic divide and extend Int and Double to support it and then use that within the member func. Thanks!

[Andreas Sinz]

kotlin is constrained by java on this one

[tylerwilson]

Then maybe when we move to the KVM. 😉 Thanks again!

[Andreas Sinz]

yeah 😂