Rare or Currently Unused Keywords
This page highlights sheets that usually need a specific architectural, ABI, macro, or low-level context before they become useful in day-to-day code review.
| Keyword | Why it is less common | Read it with |
|---|---|---|
asm | Low-level escape hatch with a narrow use case. | unsafe, share |
unsafe | Explicit risk boundary, not a default coding style. | asm, trait |
macro | Mostly relevant when extending the language surface or tooling. | proc, form |
trait | Advanced abstraction surface that appears later than core declarations. | type, form |
select | Specialized branching surface, less common than if or match. | match, when |
“Rare” does not mean “obsolete”. These sheets matter when auditing advanced code, but they are usually best read after the recommended order and the learning packs.