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macro hygiene

Variables a macro creates can't clash with variables at the place it's used.

Hygiene keeps identifiers introduced inside a macro_rules! expansion separate from same-named identifiers at the call site (for local variables and labels).

Examples

  • A macro that expands to let x = 99; leaves the caller's own x alone: after make_x!();, println!("{x}") still prints 5.

See also

declarative macro fragment specifier scope
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