Which convention is better? 1.

checkNotNull(x).also {
    // do something like..
    it.prop = y
    // ...
}

2.

x?.apply {
    // do something like..
    it.prop = y
    // ...
} ?: throw IllegalStateException()

I would favour `requireNotNull`/`checkNotNull` over a safe call and throw here because I think it more clearly and concisely expresses the hard requirement on

x

being non-null. I'd probably go with either

requireNotNull(x)
x.prop = y

or

requireNotNull(x).apply {
    prop = y
}

depending on whether or not the scoping/return value of

apply

were required in your actual use case.

Thanks for the opinion. Is a difference between

requireNotNull

and

checkNotNull

(also between

require

and

check

) only something conventional, such that one is used for checking function arguments, and one is used for checking other program states?

No problem! I'm not aware of any particular convention to be honest... I guess it's just a matter of which exception type makes the most sense. I haven't used

checkNotNull

but use

requireNotNull

mostly for things like reading from config files or validating POST requests. If my function required a non-null type I would just make that clear in the signature if possible 🙂

@Bornyls Deen technically, log statements are side-effects😉.