`take`

Returns a lazy iterable of the first length values from a source.

Iterable<A> take<A>(int length, Iterable<A> iterable) FxAsyncIterable<A> takeAsync<A>(int length, FxAsyncIterable<A> iterable) Fx<T> Fx.take(int count) // chain FxAsync<T> FxAsync.take(int count) FxEvents<T> FxEvents<T>.take(int count) // chain (events)

Lecture

take is how a lazy pipeline stays finite. It stops pulling from its source the moment it has yielded length values — the upstream never sees more requests than that. Because FxDart sources like range, repeat, and cycle can be infinite, take is often the only thing that makes a pipeline safe to run at all.

It comes as a data-first function (take(n, iterable)) and as a chain method (fx(iterable).take(n)). On the async side, takeAsync/.take() is a pass-through: it doesn't serialize the upstream, so a concurrent(n) further up the chain keeps overlapping its pulls right up until take has what it needs.

Demo 1 · Basics, and taking from an infinite source

cycle repeats its input forever — without take, iterating it would never finish:

Demo 2 · Async, still overlapping under concurrent

Only 4 values are ever pulled here, but concurrent(3) upstream still evaluates them 3-at-a-time — take doesn't force everything sequential:

Try it yourself

Exercise: take only the first 3 names from the queue.

Related: takeRight — last n instead of first n · takeWhile — take by predicate · range · cycle — infinite sources · concurrent — parallel evaluation