Do you have callbacks (and other difficult for iterators) and are you tired of .collect() them into Vecs? There is a solution.

Buter - buffered iterator with fluid buffer, which is used as a place for all iterations

Usage

```rust struct Worker { // ... }

impl Worker { fn workimpl(&mut self) -> impl Iterator + ' { callbackwork(|i| self.buf.extendone(i)); self.buf.iter() } }

struct YourType { worker: Mutex, // ... }

impl YourType { pub fn work(&self) -> impl Iterator + '_ { self.worker.lock().work_impl() } } ```

Benches

This is appropriate both with large results and with small ones test buter ... bench: 14 ns/iter (+/- 5) test vec_push ... bench: 212 ns/iter (+/- 130) test vec_push_with_capacity ... bench: 54 ns/iter (+/- 32) ``` buter time: [4.7527 ms 4.8466 ms 4.9428 ms] vecpush time: [9.6938 ms 9.8887 ms 10.086 ms] vecpushwithcapacity time: [6.5350 ms 6.6588 ms 6.7789 ms]

```