CODEWITHSUNDEEP
kotlin
Zimri Leisher
Zimri Leisher

Reputation: 1376

Checking if a KClass is an object

I have the following Kotlin code:

fun isObject(type: KClass<*>) = type.objectInstance != null

fun main() {
    println(isObject(emptyMap<Int, Int>()::class))
}

which produces the following errror:

Exception in thread "main" java.lang.IllegalAccessException: class kotlin.reflect.jvm.internal.KClassImpl$Data$objectInstance$2 cannot access a member of class kotlin.collections.EmptyMap with modifiers "public static final"
    at java.base/jdk.internal.reflect.Reflection.newIllegalAccessException(Reflection.java:361)
    at java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:591)
    at java.base/java.lang.reflect.Field.checkAccess(Field.java:1075)
    at java.base/java.lang.reflect.Field.get(Field.java:416)
    at kotlin.reflect.jvm.internal.KClassImpl$Data$objectInstance$2.invoke(KClassImpl.kt:114)
    at kotlin.reflect.jvm.internal.ReflectProperties$LazyVal.invoke(ReflectProperties.java:62)
    at kotlin.reflect.jvm.internal.ReflectProperties$Val.getValue(ReflectProperties.java:31)
    at kotlin.reflect.jvm.internal.KClassImpl$Data.getObjectInstance(KClassImpl.kt)
    at kotlin.reflect.jvm.internal.KClassImpl.getObjectInstance(KClassImpl.kt:239)

I want my isObject function to work for any arbitrary KClass but I don't know how to do it without checking if the object instance is non null. Any suggestions?

Upvotes: 4

Views: 1585

Answers (1)

fluidsonic
fluidsonic

Reputation: 4676

If you don't mind some reflection overhead and that it only works with Kotlin/JVM then you can use my library fluid-meta for that:

fun isObject(type: KClass<*>) = Meta.of(type) is MObject

Use version 0.9.16 if you're still on Kotlin 1.3 and the library won't work otherwise.

It uses the hidden Kotlin metadata annotations added to each class generated by Kotlin. If these annotations get stripped in your project at some point (e.g. by an aggressive ProGuard) then you won't have that information at runtime anymore though.

Upvotes: 1

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