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kotlinlang

I have a data class
```
data class Item(
        val children: List&lt;Item&gt;
}
```
is there a way to make a deep (recursive) copy of such an object? `item.copy()` creates a copy of the top object only but not the `children`

You can either create your own `copy` that does a deep copy or serialize and deserialize the whole instance

Also if you're going to write a deep copy function think about whether these objects can ever be recursive.

Definitely not, more often then not everything is immutable and then recursively copying would be a huge waste.

it depends on the use case; you're right, in most current uses a deep copy would be a waste, but there are use cases in which it would be useful

when the object is the primary holder of one of its properties, a deep copy is what makes the most sense, and when they're just references to something handled somewhere else, just copying the reference is the way to go

can not imagine a real life case when I want to make a copy of a data object with the `copy` method but not including all inner data objects

When your data class references a bunch of immutable objects, and you want to make a copy with one of those references changed for example.

maybe a compiler hint telling when a field is the primary reference to its contents... so during copy() calls the fields annotated with that modifier are also copied, in a recursive call

...but that would be another big language proposal haha

"think about whether these objects can ever be recursive" -- I suspect that was specifically "think about whether there could be any cycles you have to deal with"

It would be hard to justify compiler-generated code that throws overflowexceptions.