Merge two data classes in Kotlin

merge.kt

import kotlin.reflect.full.declaredMemberProperties
import kotlin.reflect.full.primaryConstructor

/**
 * Merge two data classes
 *
 * The resulting data class will contain:
 * - all fields of `other` which are non null
 * - the fields of `this` for the fields which are null in `other`
 *
 * The function is immutable, the original data classes are not changed 
 * and a new data class instance is returned.
 *
 * Example usage:
 *
 *     val a = MyDataClass(...)
 *     val b = MyDataClass(...)
 *     val c = a merge b
 */
infix inline fun <reified T : Any> T.merge(other: T): T {
    val nameToProperty = T::class.declaredMemberProperties.associateBy { it.name }
    val primaryConstructor = T::class.primaryConstructor!!
    val args = primaryConstructor.parameters.associateWith { parameter ->
        val property = nameToProperty[parameter.name]!!

        (property.get(other) ?: property.get(this))
    }
    return primaryConstructor.callBy(args)
}

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