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declarative macro

A macro written as patterns that expand into code.

macro_rules! macros match their input against patterns with fragment specifiers (expr, ident, ty, tt...) and repetitions, and expand to token trees.

Examples

  • show!(temps.len()), with ($value:expr) => { println!("{} = {:?}", stringify!($value), $value) }, prints temps.len() = 3.

See also

fragment specifier macro hygiene procedural macro
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