Set property by string in Kotlin using reflection?

Question

I have an object:

class User {
  var id: String? = null
  var name: String? = null
}

and list of pairs:

val fieldsToChange = listOf<Pair<String, String>>(Pair("name", "foo"), Pair("id", "bar"))

I would like to iterate trough list of pairs and set appropriate values for given properties using reflection.

Answer 1

Given class instance obj we can extract properties with names using obj::class.memberProperties.

We can construct a mapping from property name to property:

val nameToProperty = obj::class.memberProperties.associateBy(KProperty<*>::name)

Then we can iterate over fieldsToChange and retrieve property and set it:

fieldsToChange.forEach { (propertyName, propertyValue) ->
   nameToProperty[propertyName]
       .takeIf { it is KMutableProperty<*> } // take only "settable" (var) properties
       ?.let { it as KMutableProperty<*> } // cast it to mutable property so we can access setter
       ?.let { it.setter.call(obj, propertyValue) } // call the setter
}

Additionally, we can make this generic:

fun setFields(obj: Any, fieldsToChange: List<Pair<String, Any?>>) {
    val nameToProperty = obj::class.memberProperties.associateBy(KProperty<*>::name)
    fieldsToChange.forEach { (propertyName, propertyValue) ->
        nameToProperty[propertyName]
                .takeIf { it is KMutableProperty<*> }
                ?.let { it as KMutableProperty<*> }
                ?.let { it.setter.call(obj, propertyValue) }
    }
}

val user = User()
setFields(user, fieldsToChange)

assert(user.name == "foo")
assert(user.id == "bar")

Possible improvement would be to optimize nameToProperty to contain only MutableProperties already casted to KMutableProperty