zp-append-without-reserve — append-without-reserve
Claim
ArrayList.append in loop vs ensureTotalCapacity + appendAssumeCapacity under Zig 0.17.0 -Ofast on this Linux machine shows a clear before/after wall-clock gap.
How measured
- Harness:
packages/zperf/examples/bench/evidence_fill.zig(rulezp-append-without-reservecases) - Build:
zig build-exe -Ofast· optimize_mode=fast - Timing:
Io.Clockawake; warm=2; median of 9 rounds - before:
append_no_reserve - after:
ensure_then_assume - ops=50000
- Raw:
zp-append-without-reserve.jsonl
Runtime (this evidence file)
| Field | Value |
|---|---|
| When | 2026-10-21 Asia/Shanghai (JSONL ts is UTC) |
| Zig | 0.17.0 · fast |
| Median before | ~0.1308 ms |
| Median after | ~0.06291 ms |
| ratio before/after | ~2.08× |
Lint mapping
zperf-lint zp-append-without-reserve / append-without-reserve. Default severity in rules.zig is off (the CLI does not report the rule); see evidence-policy for keep/escalate. Evidence exists and agrees directionally.
Verdict
Agree ~2.08× for N=50k growth from empty.
Limits
When N is unknown, reserve may waste; test/arena paths are skipped by lint.