kt-string-plus-hot — string += vs buildString
Status: measured
Claim
s += in a loop is vastly slower than buildString (~521×) for N=30000 on Kotlin 2.4.21 / JDK 27.
How measured
-
Harness: EvidenceKt.kt
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Raw lines:
kt-string-plus-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 (string_plus) | 93.440375 ms |
Median after (buildString) | 0.179375 ms |
| ratio before/after | ~521× |
Lint mapping
kotlinperf-lint kt-string-plus-hot: keep default; kit-local KT* only.
Limits
- Default stays off.