Hey guys can we improve this piece of code? ```val filteredTopics by lazy { MutableStateFlow<Lis...

# codereview

[Vivek Modi]

Hey guys can we improve this piece of code?

val filteredTopics by lazy { MutableStateFlow<List<Topics>>(emptyList()) }

val temp = list.filter { it.topics != null }.filter { it.title == value.title }
filteredTopics.value = temp.firstOrNull()?.topics?.sortedBy { topic -> topic.title } ?: emptyList()

[Diego Marzo]

Hi Vivek, I believe that a small improvement could be to do both filters together, the are pretty small:

filteredTopics.value = list.filter { it.topics != null && it.title == value.title }.firstOrNull()?.topics?.sortedBy { topic -> topic.title } ?: emptyList()

[Diego Marzo]

I would (and this is 100% personal taste) do it together just with returns and nice spacing

[Vivek Modi]

Hi @Diego Marzo thank you so much.

[ephemient]

.filter { ... }.firstOrNull() == .firstOrNull { ... }
?: emptyList() == .orEmpty()

[Vivek Modi]

@ephemient Sorry I didn't understand correctly, Can you please explain me, what will go inside first filter and you comparing == so what will be come there and how it will sort my list as well?

[Diego Marzo]

filteredTopics.value = list.firstOrNull { it.topics != null && it.title == value.title }

[Diego Marzo]

You can simply "drop" filter

[Diego Marzo]

since firstOrNull will do the filtering

[Vivek Modi]

and == whatwillcomehere.firstOrNull { ... }?

[Diego Marzo]

And ".orEmpty" that I didn't know about 😄 is nice sugar to use instead of ?:emptyList()

[Diego Marzo]

filteredTopics.value = list.firstOrNull { it.topics != null && it.title == value.title }".orEmpty()" <<< THIS IS WRONG! should be like ephemient mentioned bellow:
filteredTopics.value = list.firstOrNull { it.topics != null && it.title == value.title }?.topics?.sortedBy { it.title }.orEmpty()

[Diego Marzo]

This, you should be able to use just that instead

[Vivek Modi]

Okk I'll try that.

[Vivek Modi]

Thank you so much

[Diego Marzo]

I learnt something new as well!

[ephemient]

the == have equivalent results. to match the original snippet, it would look like

filteredTopics.value = list.firstOrNull { it.topics != null && it.title == value.title }?.topics?.sortedBy { it.title }.orEmpty()

[Vivek Modi]

nice @ephemient thank you so much. It really help me.

[Vivek Modi]

Thank you once again @Diego Marzo

[Paul Woitaschek]

Why is that stateflow wrapped in a lazy?

[Vivek Modi]

for lazy initialized, Is there any problem in that?

[Paul Woitaschek]

Why do you do that?

[Paul Woitaschek]

If there is not more to it, it's just another additional allocation of the lazy and only makes the code a little bit more complex

[ephemient]

lazy has cost: additional boxing, lambda creation, reflection data, synchronization, …

[ephemient]

Chet and Romain go into this:

https://youtu.be/ULgEn3-pzzs?t=932▾

[Vivek Modi]

Okk I'll remove that.