NOTE
StringBuilder
Efficient mutable text construction, capacity, non-thread-safety, and compiler concatenation optimizations.
This is a historical learning note and may contain outdated or incomplete understanding.
StringBuilder is a mutable, non-thread-safe text builder intended for efficient incremental construction.
It keeps expandable internal storage; exact growth rules are implementation details. Supplying an estimated capacity can reduce reallocations for large known outputs.
Use it for loops or complex incremental concatenation. Simple a + b + c expressions are often compiled efficiently already, so manually rewriting every concatenation is unnecessary.