kt-list-add-hot — ArrayList empty vs capacity
Status: measured
Claim
At N=2e6 boxed Ints, empty ArrayList() + add vs ArrayList(n) measured ~2.1×.
How measured
-
Harness:
examples/bench/EvidenceKt.kt→ jar -
kotlinc 2.0.21 / JRE 21
-
Raw lines:
kt-list-add-hot.jsonl
Runtime (this evidence file)
| Field | Value |
|---|---|
| When | 2026-10-22 Asia/Shanghai (JSONL ts is UTC) |
| kotlin | 2.0.21 |
| jre | 21.0.12.1 |
Median before (list_add_empty) | 5.303875 ms |
Median after (arraylist_capacity) | 3.358458 ms |
| ratio before/after | ~1.58× |
Lint mapping
kotlinperf-lint kt-list-add-hot: keep default; kit-local KT* only.
Limits
- Boxing dominates; capacity helps some. Not a jvmperf JMH ID.
- Default stays off.