Kotlin data class: how to read the value of property if I don't know its name at compile time?

Question

How can I read the value of property in a Kotlin data class instance if the property name is only known at runtime?

Answer 1

Here is a function to read a property from an instance of a class given the property name (throws exception if property not found, but you can change that behaviour):

import kotlin.reflect.KProperty1
import kotlin.reflect.full.memberProperties

@Suppress("UNCHECKED_CAST")
fun  readInstanceProperty(instance: Any, propertyName: String): R {
    val property = instance::class.members
                     // don't cast here to , it would succeed silently 
                     .first { it.name == propertyName } as KProperty1 
    // force a invalid cast exception if incorrect type here
    return property.get(instance) as R  
}

build.gradle.kts

dependencies {
    implementation(kotlin("reflect"))
}

---

Using

// some data class
data class MyData(val name: String, val age: Int)
val sample = MyData("Fred", 33)

// and reading property "name" from an instance...
val name: String = readInstanceProperty(sample, "name")

// and reading property "age" placing the type on the function call...
val age = readInstanceProperty(sample, "age")

println(name) // Fred
println(age)  // 33