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kotlinlang

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&lt;Duration&gt;
    get() = emptySet&lt;Duration&gt;() + spans.asSequence().map({ span -&gt; span.begin })```
setOf() takes varargs, but I'm not aware of a pythonesque ability to ** an iterable argument to varargs...

```spans.mapTo(mutableSetOf()) { span -&gt; span.begin() }```
can be used as a `Set`, as long as nobody casts it back to a `MutableSet`

if you're concerned about that,
```buildSet { spans.mapTo(this) { span -&gt; span.begin() } }```
will create a Set that will throw on mutation

it is possible to
```setOf(*spans.map { span -&gt; span.begin }.toTypedArray())```
but that requires going through an Array twice (due to varargs copying)

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