I see that my team mates are using `lateinit var` ...

# announcements

[Eugen Martynov]

I see that my team mates are using lateinit var for things that should be downloaded first. Is it good practice? (I don’t like it)

[Matej Drobnič]

IMO lateinit var should only be used when there is a guarantee that variable will be initialized immediately (just not in the constructor)

[Matej Drobnič]

for example in onCreate method on Android which is called pretty much immediately after constructor

[Eugen Martynov]

Any good thoughts to explain it?

[Eugen Martynov]

I understand they don’t want to have nullable and they are trying to guard with isInitialised

[Paulius Ruminas]

What happens if download fails? It throws that variable has not been initialised? That does not seem logical from the exception.

[Eugen Martynov]

it just ignores logic that is there or tries redownload

[Paulius Ruminas]

Could you show the code? I don't understand why a lateinit var is needed if the logic is skipped on failure. Where is the variable accessed then? Or are there checks everywhere if the download succeeded?

[gildor]

My thumb of rule: if you got a case that you need isInitialised than you misuse lateinit and should use nullable instead

[gildor]

The language provides great tools to handle nullability, so it’s a lot easier and safer to use nullable, than conditional lateinit

[Paulius Ruminas]

I wonder what's the use case that they added isInitialised for because like you said if you use it you should probably use nullable type instead.

[gildor]

Because it may be needed for some rare cases, for example for libraries that set lateinit, but most probably it’s not needef for common code

[Eugen Martynov]

Thank you for comments, if it would be official Kotlin guides about usage of lateinit var then it would be great

[streetsofboston]

My rule of thumb is like Andrey's.

Only use lateinit if you don't control the object's lifecycle (eg Activity), a 3rd party library injects upon construction (eg Dagger) or a lateinit represents an expensive resources (still, prefer 'lazy' in this case).

And I agree, it's a major codesmell when you need 'isInitialized'.