kopybuilder's Introduction

KopyBuilder

This is a compiler plugin that generates a builder class for Kotlin's data class. You can get and put properties from the builder, similar to a Map, and finally build a new instance.

Usage

Gradle Setup

Currently, it supports Kotlin versions 1.8 and 1.9.

plugins {
    id("io.github.windedge.kopybuilder") version "$version"
}

Code Generation

For example, consider the following data class:

@KopyBuilder
data class User(
    val name: String,
    val email: String?
)

It will generate code like this:

public class UserBuilder: io.github.windedge.copybuilder.CopyBuilder<User> {
    override fun `get`(key: String): Any? {
        //...
    }

    override fun put(key: String, `value`: Any?) {
        //...
    }

    override fun build(): User = User(name = ..., email = ... )
}

fun User.toCopyBuilder(): CopyBuilder<User> = ...
fun User.copyBuild(initialize: CopyBuilder<User>.() -> Unit): User { /*...*/ }

You can use it as follows:

val user = User(...)
val builder = user.toCopyBuilder()
builder.apply {
    put("name", ...)
    put("email", ...)
}
val newUser = builder.build()

// Or build with copyBuild directly
val newUser = user.copyBuild {
    put("name", ...)
}

You can even use it in a reflection way, making it possible to cooperate with 3rd party libraries:

import io.github.windedge.copybuilder.CopyBuilderHost

if (CopyBuilderHost::class.isInstance(user)) {
    @Suppress("CAST_NEVER_SUCCEEDS")
    val host = user as CopyBuilderHost<User>
    val newUser = host.copyBuild {
        put("name", "Max")
    }
}