[deadstrobe5]

Summary

Array.__delitem__ (used by del, pop() and remove()) and Array.add_line() rebuilt the whole position-to-group index map after every call, so emptying a long array with pop() or building one with add_line() per item was quadratic. This applies the approach from #666 (append) to these two methods.

After deleting a single item, only the entries after the removed position shift down by one. In add_line() the new groups always land after every existing value (at the end, or just before a trailing whitespace group, which is never indexed), so only the new values get an index. Both shortcuts keep the same guard as #666: when the map length does not match the array, or for slice deletes, they fall back to _reindex().

Same-process A/B on CPython 3.14, 7 alternating rounds, median:

Workload	Before	After	Speedup
pop() until empty, 2000 items	816 ms	21.2 ms	38x
pop() until empty, 200 items	7.92 ms	1.76 ms	4.5x
add_line() x 2000	1033 ms	35.2 ms	29x
add_line() x 200	10.7 ms	3.80 ms	2.8x
pop() until empty, 10 items	0.190 ms	0.197 ms	same

A differential fuzz of 3000 random edit sequences (pop, del with indexes and slices, remove, insert, append, add_line, setitem, extend, clear) on single-line, multiline, comment-heavy and comma-first arrays gave the same as_string(), values, index map and exceptions after every step. The new tests delete and add lines in commented arrays and then index into them.

Duplicate Check

• I searched the open PRs and found none that already fixes this issue.
• Related open PRs (if any, and why this PR is still needed): Normalize array indices before updating formatted storage #657 normalises the key at the top of __delitem__ and Fix appends after standalone array comments #680 changes appends after comments; neither touches the index rebuild at the end of __delitem__ or in add_line().

Agent Drafting Metadata

• Agent: Claude Code
• Model: Claude Opus 5.5
• Notes: the agent profiled the array paths, wrote the change and the tests, and ran the comparisons and benchmarks above. Human attestation is pending.

[human-attestation]

🛡️ Human Attestation required. A human needs to confirm this PR once before it can merge.

Attest this PR — sign in with GitHub, pass the challenge, and confirm one of the statements.