I have a data class foo ```kotlin data class Foo( ...

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[KyooSik Lee]

I have a data class foo

kotlin
data class Foo(
    val a: Int,
    val b: String,
    val c: Int
    val d: Int
) {}

And I have another data class partialFoo, where I have partial fields of foo

kotlin
data class PartialFoo(
    val a: Int,
    val b: String
) {}

Is there any way that I can copy the fields of class instance of Foo to class instance of PartialFoo?

[Kirill Zhukov]

nothing magical that I can think of

[Kirill Zhukov]

extension function Foo.toPartialFoo() might the most idiomatic

[Kirill Zhukov]

Also could use inheritance but I’d avoid it

[Kirill Zhukov]

depends on your use case of course

[KyooSik Lee]

Thanks Kirill, what do you think about using objectMapper of Spring Boot?

[Kirill Zhukov]

not familiar

[Kirill Zhukov]

quick google tells me it’s part of jackson

[Kirill Zhukov]

you could serialize your Foo object to json and then deserialize it to PartialFoo

[Kirill Zhukov]

would advice against that heh

[Kirill Zhukov]

for the purposes of what you are trying to do I don’t think it’s worth doing serialization twice

[KyooSik Lee]

That was what I thought initially. Surely extension function should be best

[KyooSik Lee]

I agree

[KyooSik Lee]

Thank you, really helped

[Kirill Zhukov]

np

[Kirill Zhukov]

another big problem with using serialization in this case is maintenance. if signature of Foo or PartialFoo changes you won’t catch until in runtime or in unit tests if you have them. You could remedy that by using hardcoded serialized names but that’s just too much trouble and still doesn’t prevent someone from deleting the field or changing the type.

[Kirill Zhukov]

with extension function you have compile time safety

[Kirill Zhukov]

let compiler help you 🙂

[bodiam]

something like MapStruct might be an option perhaps?

[Stephan Schroeder]

just stating the obvious, but your solution - if you ever find one - might well be more complex and definitely less idiomatic than a bunch of assignments in a mapper method.