what's the idiomatic way to create a Set (immutabl...

# android

[Travis Griggs]

what's the idiomatic way to create a Set (immutable) from a collection mapping operation? The following works, but seems kind of round about:

val beginEdges: Set<Duration>
    get() = emptySet<Duration>() + spans.asSequence().map({ span -> span.begin })

setOf() takes varargs, but I'm not aware of a pythonesque ability to ** an iterable argument to varargs...

[ephemient]

spans.mapTo(mutableSetOf()) { span -> span.begin() }

can be used as a Set, as long as nobody casts it back to a MutableSet

[ephemient]

if you're concerned about that,

buildSet { spans.mapTo(this) { span -> span.begin() } }

will create a Set that will throw on mutation

[ephemient]

it is possible to

setOf(*spans.map { span -> span.begin }.toTypedArray())

but that requires going through an Array twice (due to varargs copying)

[ephemient]

I assume your real usage is more complex, because in your example you could simply have used the fun <T> Sequence<T>.toSet(): Set<T> extension…