Declarative macros (macro_rules!) for code generation

Marcus Chen Jan 2026

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macro_rules! create_function {
    ($func_name:ident) => {
        fn $func_name() {
            println!("Called {}", stringify!($func_name));
        }
    };
}

create_function!(foo);
create_function!(bar);

fn main() {
    foo();
    bar();
}

1 file · rust Explain with highlit

Declarative macros (macro_rules!) let you write code that writes code, reducing boilerplate. They pattern-match on token trees and expand at compile time. I use them for repetitive patterns like implementing traits for multiple types or generating test cases. Macros are hygienic: they don't accidentally capture variables from the calling context. The syntax takes some getting used to ($(...)* for repetition, $var:ty for type arguments), but it's powerful once you learn it. For complex code generation, procedural macros (derive, attribute, function-like) are more flexible but harder to write. I reach for macro_rules! when I need simple repetition and procedural macros when I need to parse attributes or introspect types.