A modern programming language that makes developers happier.

kotlinlang

looking for a flow operator that does something like

input: Foo
output: List&lt;Foo&gt;

everytime the upstream flow emits, the operator would emit a list of this value and any previous values that are emitted

```.scan(emptyList&lt;Foo&gt;()) { list, element -&gt; list + element }```

Untitled

this is O(N), if it matters to you (but it may not)

If performance is critical I would definitely run benchmarks.
It’s a good idea to use a shared list where the elements already emitted are never replaced.

I’d use a `MutableList` instead of array though and let the stdlib handle the expansion. `ArrayList` implementation is incredibly fast.

the problem is that you need something like `.subList()` to avoid copying

otherwise all earlier flow emissions are invalidated when you mutate the list, which I believe breaks expectations

but extending mutable list will cause any earlier `.subList()` values to break with ConcurrentModificationException

hence the manual array extending and list wrapping