Why is it not possible to have a custom getter on `lateinit`? I use `isInitialized` everytime I acce...

# getting-started

[A Gamal]

Why is it not possible to have a custom getter on lateinit? I use isInitialized everytime I access lateinit, so I wonder if I could optimize that and only do the check once. In case of a nullable type, I could do something like that.

[nfrankel]

not sure i understood your question
but have you looked at lazy delegates?

[Pavlo Liapota]

Why are you using lateinit if you always check isInitialized? Just use nullable type and check != null.

And why do you throw exception in your example? Just use lateinit and exception will be thrown if field is not initialized.

[A Gamal]

Is it possible to throw a custom exception on `lateinit`if it’s not initialized? Because that’s exactly what I’m trying to do, calling isInitialized once and throw a custom exception if not initialized, same if it would be nullable type in code snippet.

[nfrankel]

it’s by default
you’ll have a NotInitializedException if i remember correctly

[A Gamal]

Yep, and if it would a nullable type, I would need to use the safe call operator at every time I access the object. But I do believe it should be lateinit as the object is being set later in a setter and MUST not be null.

[Pavlo Liapota]

So why do you need custom exception here?
If your really need it, you can write your own property delegate, see Delegates.notNull as an example.

[A Gamal]

Because I’m working on a library and would be better to have more descriptive message along side the exception.

[A Gamal]

Yep, something like Delegates.notNull would work. Thank you.

[Mike]

lateinit is generally used as a ‘hint/helper’ to the compiler that this variable will be non-null BUT isn’t getting set at construction time.

Very commonly used with DI frameworks so can define the dependency as non-null BUT it gets defined later.

What you’re doing is not a good candidate for lateinit IMO. If the consumer of the library needs to pass it, make the variable non-null, check it, and throw your exception.

If it is null, then after the !null check, you can reference it as non-null.

[A Gamal]

@Mike Totally agree with you. But when working on a library that will be used be other developers, I must well define if some methods take nullable objects or not, specifically when there’s not guarantee if some method is called before the setter method.
Hence, I prefer using delegates in this case, in which I could define that this method not accepting nullable object and could throw custom exception in case some other methods are called before init that object.

[Mike]

I understand that, just don’t feel lateinit is the way to ‘solve’ it. Are you worried about interop with Java? I must assume so as otherwise you wouldn’t need to ‘jump through hoops’.

I would suggest EITHER taking a null as the parameter, and doing null checking in Kotlin with custom exception (as you want a custom exception) OR annotate with @Nonnull annotations, and let consumers know they must pay attention.

[Mike]

And backing up, are you using lateinit on a function parameter? That’s not clear, so I may be completely off here.

[A Gamal]

No, I use Delegates.notNullOrException as extension function, so I could do something like that private var config: Config by Delegates.notNullOrException(errorMessage = "configurations must be set")