insertAt

Insert value at visible position index (0 = prepend before first visible element). Computes the after id from the current visible sequence.

Reading visibleSequence forces sequence, so the materialized list is in hand for free and is offered to the threading guard (#2193) — an append-at-the-end insertAt loop therefore computes the order once rather than once per call. A prepend or a mid-sequence insert fails the guard and the next call recomputes, exactly as before.

Throws