Is there a specific reason why `Set<T>.map {...

# stdlib

[mbonnin]

Is there a specific reason why Set<T>.map {} returns a List and not a Set ?

[Zach Klippenstein (he/him) [MOD]]

You can look at the definition of the extension function, I think it’s defined on Iterable so List is the return type that makes the most sense given the generic receiver.

[mbonnin]

Right, there's no Set<T>.map {} ...

[mbonnin]

Only Iterable<T>.map {}

[mbonnin]

I thought maybe there were considerations that a List is faster than a Set

[Ruckus]

Also, even if it was defined on Set, it wouldn't necessarily make sense to return a set, as we don't know if the mapping function will return unique values. So dropping data when mapping to a set should be explicit.

[mbonnin]

@Ruckus right, makes sense

[mbonnin]

Well, it could return a Set of a different size I guess

[Zach Klippenstein (he/him) [MOD]]

A set can’t contain duplicate values, by definition

[mbonnin]

Mmm right, and since the order or iteration is not defined, what data is going to be dropped would not be defined either

[jw]

If you want a set, use mapTo and supply one