Kotlin: Check if lazy val has been initialised

Question

Is there a way to tell if a lazy val has been initialised in Kotlin without initialising it in the process?

eg if I have a lazy val, querying if it is null would instantiate it

val messageBroker: MessageBroker by lazy { MessageBroker() } if (messageBroker == null) {     // oops } 

I could potentially use a second variable, but that seems messy.

private var isMessageBrokerInstantiated: Boolean = false val messageBroker: MessageBroker by lazy {     isMessageBrokerInstantiated = true     MessageBroker() }  ...  if (!isMessageBrokerInstantiated) {     // use case } 

Is there some sexy way of determining this, like if (Lazy(messageBroker).isInstantiated())?

Related (but not the same): How to check if a "lateinit" variable has been initialized?

Answer 1

There is a way, but you have to access the delegate object which is returned by lazy {}:

val messageBrokerDelegate = lazy { MessageBroker() } val messageBroker by messageBrokerDelegate  if(messageBrokerDelegate.isInitialized())     ... 

isInitialized is a public method on interface Lazy<T>, here are the docs.

Answer 2

Since Kotlin 1.1, you can access a property delegate directly using .getDelegate().

You can write an extension property for a property reference that checks that it has a Lazy delegate that has already been initialized:

/**  * Returns true if a lazy property reference has been initialized, or if the property is not lazy.  */ val KProperty0<*>.isLazyInitialized: Boolean     get() {         if (this !is Lazy<*>) return true          // Prevent IllegalAccessException from JVM access check on private properties.         val originalAccessLevel = isAccessible         isAccessible = true         val isLazyInitialized = (getDelegate() as Lazy<*>).isInitialized()         // Reset access level.         isAccessible = originalAccessLevel         return isLazyInitialized     } 

Then at the use site:

val messageBroker: MessageBroker by lazy { MessageBroker() }  if (this::messageBroker.isLazyInitialized) {     // ... do stuff here } 

^{This solution requires kotlin-reflect to be on the classpath. With Gradle, use
compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"}

^{The isAccessible = true part is required for the .getDelegate(), because otherwise it cannot access the private field storing the delegate reference.}