data class Post(
        val id: String,
        val content: String,
        val timestamp: Long,
        val photos: List<String>
) : Model()

data class FullPost(
        val id: String,
        val content: String,
        val timestamp: Long,
        val photos: List<String>,
        val postedBy: User,
        val with: List<User>,
        val checkedIn: Restaurant,
        val actType: String,
        val likesCount: Int
) : Model()

Is there a better way to copy the fields of Post to FullPost? So that I don't have to repeat fields like this

Nothing Kotlin-specific, but utils for Java in general are aplenty, choose whichever you like more, search for BeanUtil(s) copy properties or something like that.

You can use map and use property delegation to the map, and then copy map used by other class.

basically either use a lib which can do this, or implement it yourself, e.g. map delegation, like Olekss proposed, reflection.

Any annotation based library for this that plays well with data class?

why can’t you just make

FullPost

to extend

Post

?

data class can't be open

Ah haven’t notice it. Maybe you can make

Model

to be a

sealed class

and move common fields there?

Is this pattern usable for you?

data class FullPost(val basisPost: Post
        val postedBy: User,
        val with: List<User>,
        val checkedIn: Restaurant,
        val actType: String,
        val likesCount: Int
) : Model()

nope

Any annotation based library for this that plays well with data class?

You don't need annotations, seems pretty simple case. You could use something like Apache commons-beanutils

copyProperties

works on objects. I want it on classes. What I have in mind is something like

data class Post(
        val id: String,
        val content: String,
        val timestamp: Long,
        val photos: List<String>
) : Model()

@CopyProperties(Post::class)
data class FullPost(
        val postedBy: User,
        val with: List<User>,
        val checkedIn: Restaurant,
        val actType: String,
        val likesCount: Int
) : Model()

Uh, then you have two solutions: code generation or byte code manipulation based on annotations. Research #kapt

thanks

I think it will work quite nicely if you add delegation to the

basisPost

parameter in @hallvard's solution. It works only if

Model

is an interface though. Like this:

data class FullPost(val basisPost: Post
        val postedBy: User,
        val with: List<User>,
        val checkedIn: Restaurant,
        val actType: String,
        val likesCount: Int
) : Model() by basisPost

@aeruhxi you could use composition