In the other thread: Andrei said:
.flush() or .done() to mark the end of several writes
similar to my finish
.clear() to clear the range (useful if e.g. it's implemented as aslice with appending)
similar to my start, but start is allowed to do required initializtions too whereas clear doesn't sound as required.
Dmitry said:
.reserve(n) to notify underlying sink that it n items are coming (it should preallocate etc.)
yes, this may also be a noop on some objects
