String Concat In Loop (ARCH8070)

Key kotlin.performance.string-concat-in-loop · Severity warning · Category performance

Flags += string accumulation inside a loop - quadratic copying.

Incorrect

var out = ""
for (p in parts) out += p

Correct

val out = buildString { for (p in parts) append(p) }

Fix

Use buildString / StringBuilder, or joinToString.