Hi. I need help.. There are some code like this

Observable.something()
    .map {
        mutableList.apply {
            addAll(list)
        }
    }

Console says

UnnecessaryApply

.. But I need

return MutableList

I don't know if this is really wrong. How can I fix it? Thank you for reading..

would

Observable.something().map { mutableList.addAll(list) }

not be enough

In this case, addAll returns Unit

.also{}

will do the same job, will not be flagged and will also be a better fit here imho as you’re having a side effect.

https://kotlinlang.org/docs/reference/scope-functions.html#apply Thank you for your response.. When I read this document, I think that

apply

is more correct it this case. How about this case

Observable.something()
    .map {
        Person("Adam").apply {
            age = 32
            city = "London"        
        }
    }

Is there any flag? I can't found about that..

Is there any flag?

What do you mean?

Is there any flag?

mean

Is there any difference in

also, apply

except

it, this

Do you mean that

addAll

is a function, which can cause side effect? It understood. I also have second case like

Person().apply{ age = 32 }

It would be happy if

age

went into the constructor, but it is difficult to do so. Is it better to use aslo if there is only one line even for field set?

Is there any difference in

also, apply

except

it, this

No there are no other difference other the one you mentioned.

I think that this is a false positive... If we are using the return value it's nothing wrong with using apply. As far as I see in the tests we are not testimg this case and we should.

I don’t like this code that much because you should not use mutable objects in a stream but that’s out of the scope of detekt and the issue.

Agree. That’s also the root cause of the problem actually. Ideally RxJava would have an operator like

onEach

or similar

It does,

doOnNext

I’m really rusty with RxJava, but would this be equivalent? 🤔

Observable.something()
    .doOnEach {
        mutableList.addAll(it)
    }

No, you still emit it instead of the updated mutableList