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kotlinlang

I've implemented the plus method on a data class and want to sum up all classes using
```containers.sumOf { it.dataClassImplementingPlus }```
Why isn't this working? What am I looking for? Is there anything better than:
```containers.map { it.dataClassImplementingPlus }
    .fold(DataClassImplementingPlus()) { acc, el -> acc + el },```


There is no "summable" interface so you don't get these `sumOf` extensions for free. You can implement your own like you did, though. I did exactly that there:  <https://github.com/joffrey-bion/accounting/blob/main/money%2Fsrc%2FcommonMain%2Fkotlin%2Forg%2Fhildan%2Faccounting%2Fmoney%2FAmount.kt#L93|https://github.com/joffrey-bion/accounting/blob/main/money%2Fsrc%2FcommonMain%2Fkotlin%2Forg%2Fhildan%2Faccounting%2Fmoney%2FAmount.kt#L93>

on a side note related to your code, you can use `reduce` instead of `fold`, this way you don't need to create starting accumulator element

explodes if the list is empty though, right?

<@U02Q05JJF7S> what if the list is empty?

oh yes, if you need to cover the empty case as well, then either `fold` or `reduceOrNull` would work depending on the context