Hello how could i do this better

# codereview

[Alexis Cala Martínez]

Hello how could i do this better

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[Alexis Cala Martínez]

is this better?

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[Matteo Mirk]

You can further simplify this by providing just the key selector to associateBy and avoid referencing the concrete implementation:

val mapSomeDTO = getSomeDTOList().associateBy { it.id }

[Alexis Cala Martínez]

hello @Matteo Mirk good morning, thx for aswering

[Alexis Cala Martínez]

but i want a hashmap

[Matteo Mirk]

why do you need to reference the concrete class instead of its interface?

[Matteo Mirk]

in general you should prefer coupling to interfaces instead of implementations, but if you really have some reason for it, just use the other associateByTo overload

val hashMapSomeDTO = getSomeDTOList().associateByTo(HashMap()) { it.id }

[Alexis Cala Martínez]

What i really want is returning a map because later i have to used for complete another response, in order to do not use a find on a list i rather a hashmap, but really i want to decrease from O(n^2) to O(n)

[Matteo Mirk]

I see, so there’s no reason to couple the client code to a specific implementation (HashMap), you can safely return a Map reference if all you need is a fast lookup by id.
[By the way, a linear search on a list has an average complexity of O(n), but you can use a binary search which is O(log n)]

[Alexis Cala Martínez]

yes for sure but elements on list are not ordered

[Matteo Mirk]

Ah yes, sorry I overlooked that. Anyway you don’t start from O(n^2) complexity