There are 2 methods of creating empty collections,...

# announcements

[andrzej]

There are 2 methods of creating empty collections, e.g. for a set:
1. emptySet()
2. setOf()
I know these two are equivalent (implementation is identical), but what is the more idiomatic Kotlin way? Is there any reason why 2 solutions exist for the same issue? I know this question might sound silly but we have a code base where both ways are used and want to get rid of one of them once and for all.

[Hanno]

setOf takes a vararg which is why you can ommit any params, but if your intention is to create a set without any elements, emptySet is probably the correct way

[Michael de Kaste]

use setOf() wherever you are actually using something where you don't know if the standard size of that set might be bigger than 0 in the future, so in the future you could theoretically have: setOf("someValue", "someOtherValue")

emptySet() is an explicit empty set. Use this if this is truly the intention of your logic.

[andrzej]

@Hanno nope, here is setOf implementation:

@kotlin.internal.InlineOnly
public inline fun <T> setOf(): Set<T> = emptySet()

[Michael de Kaste]

that's just filler code because varargs takes additional bytes/logic.

This ensures that setOf without arguments is still as fast as possible

[marstran]

@Michael de Kaste setOf creates a read only set, so it won't get bigger in the future.

[Michael de Kaste]

it's the same reason why, in java, I know that some standard libraries they make functions for every size up to 10 or something

[Michael de Kaste]

@marstran, yes I know. I used the example to show that maybe you don't know in the future of the intention of the set would be to always be empty at first.

e.g; val invalidStrings = setOf()

maybe in the future you might want to change this standard set to setOf("thisIsInvalid", "thisToo")

[Dico]

I would discourage the use of setOf() in general.

[Dico]

Only when you're doing something like

val someSpecialStrings = setOf(
)

[Dico]

The problem is that without any parameters, the element type can't be inferred, so there's little point having this function.

[Daniel]

Function should be

setOf(first: T, vararg ensuing: T)

Dont know why they decided against it.
Other than that: emptySet() is most likely a fallback of some sort. So best be explicit and call it emptySet(). The empty immedeately conveys the meaning
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